Adding memory to a 2017 IMac - clear advice for a non-tech person please

Is your iMac a 27" or 24" model? The 24" models can't be upgraded memory wise by the user. It would have to be taken into an Apple Authorized Service Provider for replacement and would not be inexpensive. 

But, as Jack-19 has told you it's to memory that will speed up a Mac but a faster drive.

Run Etrecheck and post the report as follows:

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can evaluate the report to see if we can determine the cause of the problem.

Assuming it's the 27" Retina, it's easy to add RAM, here's an install video...

How to Install Memory in a 27-Inch iMac Late 2015-2020 (macsales.com)

Memory Upgrades for 2017 iMac 27-Inch (macsales.com)

Amazon.com: OWC 16GB PC19200 DDR4 2400MHz SO-DIMM Memory Compatible with Mid 2017 iMac 27" w/Retina 5K Models and Compatible PCs (OWC2400DDR4S16G) : Everything Else

Crucial 16GB Single DDR4 2400 MT/s (PC4-19200) DR x8 SODIMM 260-Pin Memory - CT16G4SFD824A (amazon.com)

Hi there!

If your Mac runs slowly, adding memory often doesn't help.

Rahter, I believe you should create an EtreCheck report. EtreCheck is a simple, helpful utility to diagnose and identify both software and select hardware issues.

If your Mac is experiencing an issue, such as poor performance or running slowly, kernel panics, apps freezing or quitting unexpectedly, storage issues, and many more, generating an EtreCheck report is a great place to start for troubleshooting issues with your Mac while getting help at Apple Support Community. EtreCheck was developed by a highly respected member of these very Apple Support Community forums, and it is trusted by many users.

Downloading

To get started, download EtreCheck:

https://etrecheck.com/en/welcome.html

Click “download” on the site. The app will be downloaded to your Mac to your downloads location, which is the “Downloads” folder by default. This can be accessed by going to the Finder > Go (in the top menu bar) > Downloads.

Open the app, and generate a report

Open the downloaded application, and follow the initial steps to open the app. Choose a problem in the drop-down menu, and click Start. Creating a report typically takes 2-4 minutes on a healthy Mac.

View your report, and upload a copy to Apple Support Community

Once you have your report generated, you can upload it to Apple Support Community for us to review and provide suggestions. Please refer to this document with instructions for uploading your report and using the “Additional Text” function of Apple Support Community:

How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report - Apple Community

If you need help in the meantime, please let us know!

Jack

OWC has partner firms in Australia:

https://www.owc.com/partners/where-to-buy

Crucial does not show an AUS site:

but you can see what the UK site shows for shipping destinations.

Please DO NOT buy any RAM other than Crucial or OWC. Other brands have long histories of not being good for Macs.