iMac running very slowly.

I have an iMac 21.5-inch mid-2011. We noticed a sharp dropoff in its speed a few months ago and have seen it gradually slow from there. It is now at the point where we need to do something, but I'm hoping the problem is fixable and we don't need to just replace it. It only has 4 GB or RAM so I have considered adding RAM. I did run Etrecheck and this is the report I received:

EtreCheck version: 4.0.4 (4A150)

Report generated: 2018-02-28 10:59:21

Download EtreCheck from https://etrecheck.com

Runtime: 10:48

Performance: Poor

Problem: Computer is too slow

Major Issues:

Anything that appears on this list needs immediate attention.

Hardware failure - Your machine shut down due to a hardware failure.

Poor performance - EtreCheck report took over 10 minutes to run. This is very unusual.

Minor Issues:

These issues do not need immediate attention but they may indicate future problems.

Upgradeable RAM - This machine has upgradeable RAM that would help its performance.

Clean up - There are orphan files that could be removed.

Unsigned files - There is unsigned software installed. It appears to be legitimate but should be reviewed.

System modifications - There are a large number of system modifications running in the background.

Hardware Information:

iMac (21.5-inch, Mid 2011)

iMac Model: iMac12,1

1 2.5 GHz Intel Core i5 (i5-2400S) CPU: 4-core

4 RAM Upgradeable

BANK 0/DIMM0

2 GB DDR3 1333 ok

BANK 1/DIMM0

2 GB DDR3 1333 ok

BANK 0/DIMM1

Empty

BANK 1/DIMM1

Empty

Video Information:

AMD Radeon HD 6750M - VRAM: 512 MB

iMac 1920 x 1080

Drives:

disk0 - WDC WD5000AAKS-402AA0 500.11 GB (Mechanical)

Internal SATA 3 Gigabit Serial ATA

disk0s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk0s2 - Macintosh HD (Journaled HFS+) 499.25 GB

disk0s3 - Recovery HD (Journaled HFS+) [Recovery] 650 MB

disk1 - Iomega External HD 1.00 TB

External USB 480 Mbit/s

disk1s1 32 KB

disk1s3 - B*****p (Journaled HFS+) 1.00 TB

Mounted Volumes:

disk0s2 - Macintosh HD 499.25 GB (172.01 GB free)

Journaled HFS+

Mount point: /

disk1s3 - B*****p 1.00 TB (334.29 GB free)

Journaled HFS+

Mount point: /Volumes/B*****p

Network:

Interface modem: Internal Modem

Interface fw0: FireWire

Interface en1: AirPort

802.11 a/b/g/n

One IPv4 address

3 IPv6 addresses

Interface en3: Bluetooth PAN

Interface en0: Ethernet

Interface en4: iPhone

Interface bridge0: Thunderbolt Bridge

iCloud Quota: 15.42 GB available

System Software:

macOS Sierra 10.12.6 (16G1036)

Time since boot: Less than an hour

System Load: 1.71 (1 min ago) 1.53 (5 min ago) 1.05 (15 min ago)

Security:

Unsigned Files:

Launchd: /Library/LaunchDaemons/com.microsoft.office.licensing.helper.plist

Executable: /Library/PrivilegedHelperTools/com.microsoft.office.licensing.helper

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchAgents/com.citrix.ReceiverHelper.plist

Executable: /usr/local/libexec/ReceiverHelper.app/Contents/MacOS/ReceiverHelper

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchAgents/com.hp.help.tocgenerator.plist

Executable: /Library/Documentation/Help/Hewlett-Packard/TOCGenerator.app/Contents/MacOS/TOC Generator

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchAgents/com.citrix.ServiceRecords.plist

Executable: /usr/local/libexec/ServiceRecords.app/Contents/MacOS/ServiceRecords

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchAgents/com.citrix.AuthManager_Mac.plist

Executable: /usr/local/libexec/AuthManager_Mac.app/Contents/MacOS/AuthManager_Mac

Details: Exact match found in the whitelist - probably OK

Kernel Extensions:

/Library/Extensions

[Not Loaded] CitrixGUSB.kext (1.0)

[Loaded] SymXIPS.kext (8.1 - SDK 10.10)

[Loaded] SymInternetSecurity.kext (7.6.1 - SDK 10.11)

[Loaded] SymIPS.kext (7.6.1 - SDK 10.11)

[Loaded] NortonForMac.kext (7.6.1 - SDK 10.11)

/System/Library/Extensions

[Not Loaded] MaxtorPowSecDriver.kext (1.0.0)

[Not Loaded] LfEtherConfig.kext (2.0)

[Not Loaded] LfConnectDriver.kext (1.8.1 - SDK 10.7)

[Not Loaded] IOFireWireMxBt.kext (2.0.0)

[Not Loaded] HotSync Classic Seize.kext (3.2.1)

Startup Items:

MxBtDaemon Path: /Library/StartupItems/MxBtDaemon

Qmaster Path: /Library/StartupItems/Qmaster

RetroRun Path: /Library/StartupItems/RetroRun

System Launch Agents:

System Launch Daemons:

Launch Agents:

Launch Daemons:

User Launch Agents:

User Login Items:

Monitor Application

(/Applications/LeapFrogConnect.app/Contents/Monitor.app)

Firefox Application (Mozilla Corporation

(/Applications/Firefox.app)

Fitbit Connect Menubar Helper Application (Fitbit, Inc. - installed 2017-10-02)

(/Applications/Fitbit Connect.app/Contents/MacOS/Fitbit Connect Menubar Helper.app)

HP Device Monitor SMLoginItem (Hewlett Packard - installed 2016-08-31)

(/Library/Printers/hp/Frameworks/HPDeviceMonitoring.framework/Versions/1.0/Help ers/HP Device Monitor Manager.app/Contents/Library/LoginItems/HP Device Monitor.app)

Internet Plug-ins:

Unity Web Player: UnityPlayer version 4.6.5f1 (installed 2015-05-04)

Flip4Mac WMV Plugin: 2.0.2.10 (installed 2006-06-12)

AdobePDFViewerNPAPI: 17.012.20098 (installed 2018-02-24)

FlashPlayer-10.6: 28.0.0.161 (installed 2018-02-06)

PDF Browser Plugin: 2.4.4 (installed 2012-04-16)

Silverlight: 5.1.20513.0 (installed 2013-07-27)

QuickTime Plugin: 7.7.3 (installed 2017-11-16)

Flash Player: 28.0.0.161 (installed 2018-02-06)

CitrixICAClientPlugIn: 12.1.0 (installed 2015-10-27)

SharePointBrowserPlugin: 14.7.3 (installed 2017-04-12)

AdobePDFViewer: 18.011.20038 (installed 2018-02-24)

CouponPrinter-FireFox_v2: Version 1.1.6 (installed 2011-09-20)

iPhotoPhotocast: 7.0 (installed 2012-04-06)

DirectorShockwave: 12.2.4r194 (installed 2016-02-22)

User Internet Plug-ins:

fbplugin_1_0_3: Unknown (installed 2010-02-25)

WebEx64: 1.0 (installed 2014-06-28)

3rd Party Preference Panes:

Flash Player (installed 2018-02-01)

Flip4Mac WMV (installed 2007-08-24)

Time Machine:

Skip System Files: No

Mobile backups:

Auto backup: Yes

Volumes being backed up:

Macintosh HD: Disk size: 499.25 GB - Disk used: 327.24 GB

Destinations:

I*******D [Local] (Last used)

Total size: 1.00 TB

Total number of backups: 150

Oldest backup: 2013-08-02 12:18:02

Last backup: 2018-02-25 17:29:38

Top Processes by CPU:

Top Processes by Memory:

Top Processes by Network Use:

Top Processes by Energy Use:

Virtual Memory Information:

Clean up:

~/Library/LaunchAgents/com.adobe.ARM.202f4087f2bbde52e3ac2df389f53a4f123223c9cc5 6a8fd83a6f7ae.plist

/Applications/Adobe Reader.app/Contents/MacOS/Updater/Adobe Reader Updater Helper.app/Contents/MacOS/Adobe Reader Updater Helper

Executable not found

Diagnostics Information (past 7 days):

2018-02-28 10:35:06 Last Shutdown Cause: -128 - Unknown

2018-02-28 09:58:42 Quicken 2015.app Crash

2018-02-21 18:16:39 spindump Crash

End of report

Does anyone have advice to help speed things up? Thanks so much for the help!