Can I upgrade my iMac's RAM from 2x4GB to 2x8GB?

"disassembled".

Are you wanting more RAM because your iMac is slow? Most reports here of slow iMacs, especially 21.5" models made between 2012 and 2019, are not due to RAM or a lack thereof.

Do this little quiz:

—is the computer slow to start up (cold boot)?

—are large apps slow to open?

—once open, do those apps seem to work at expected speed?

If you say "yes" three times, you have a storage problem, not a RAM problem. Most entry-level iMacs 21.5" 2012-2019 were fitted with a. slow and under-spec mechanical hard drive. It was never after one new, and the seem to struggle with newer versions of macOS.

All the RAM th the world cannot speed up an underperforming hard drive.

Yes and no. A 21.5" 2017 iMac would have to be dissembled in order to reach the RAM slots. Not something a user should do.

You're welcome.

Spending time and money on an obsolete Mac does not make a great deal of sense, particularly a 2017 21.5" model.