upgrading my iMac

macOS High Sierra - Technical Specifications

General Requirements

• OS X 10.8 or later
• 2GB of memory
• 14.3GB of available storage to perform upgrade*
• Some features require an Apple ID; terms apply.
• Some features require a compatible Internet service provider; fees may apply.

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac. These Mac models are compatible with macOS High Sierra:

• MacBook (Late 2009 or newer)
• MacBook Pro (Mid 2010 or newer)
• MacBook Air (Late 2010 or newer)
• Mac mini (Mid 2010 or newer)
• iMac (Late 2009 or newer)
• Mac Pro (Mid 2010 or newer)
• Don't use FireFox for these links…

https://support.apple.com/kb/sp765?locale=en_US

https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=12

Hello, Sacramento.

How to Upgrade  macOS:

The macOS version you can upgrade to depends on the model and year of your Mac. Click the  (Apple) menu at the top left of your screen and choose About This Mac. 

❗️ – IMPORTANT – Backup your data. (You’ve been warned.)

Learn How to Back up your Mac with Time Machine:

https://support.apple.com/en-us/HT201250

🖥 – Check compatibility of your Mac with newer versions of macOS.

https://support.apple.com/en-us/HT201475

✅ - Using Safari only, download the macOS upgrade installer:

Click > High Sierra.

EDIT - deleted 32-bit app warning. Irrelevant.