How to upgrade memory in iMac (Retina 4K, 21.5-inch, 2017)?

That iMac has two RAM slots, but they are sealed in and not user-accessible. Cutting the Mac open and resealing it afterwards is not a job for the faint – so professional installation would be recommended.

As for RAM, Macs can be picky about RAM, so I would suggest having the shop get the RAM which is to be installed from Other World Computing.

Other World Computing – OWC Memory Upgrades For 21.5" iMac with Retina 4K & Non-Retina Display (2017)

Yes, why do you want more RAM/memory? If to "speed up" the computer, you'll most likely be wasting money.

Long history here teaches that "slow" 21.5-inch iMacs made between 2012 and 2019 are not starved for RAM but suffering from either:

— the slow, laptop-class mechanical hard drive that was the base iMac storage or,

— a malfunction with the optional Fusion drive system.

Th EtreCheck report that D.O. Johnson has wisely recommended will show the storage type you have, its current performance, and give indications of drive health. It is likely with that report we can identify the problem with one more post from you and give action recommendations.

There is also a little three-question test:

— Is the computer slow to cold-start?

—Are big apps liie MS Offfine or Photoshop slow to launcj?

— Once launched. do thse big apps seem to run acceptably?

Three "Yes" answers suggest your storage, not a paucity of RAM, is the culprit.

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stevewalls0311 wrote:

How do I upgrade memory in iMac (Retina 4K, 21.5-inch, 2017?

How much RAM is currently installed in the computer?

Why are you considering adding more?

If your Mac seems to be running poorly, then simply adding additional RAM is not typically the solution to that problem.

You can use the Activity Monitor app to determine how well the Mac is using the RAM it has.

Activity Monitor User Guide for Mac - Apple Support

Launch the app and take a look at the Memory Pressure graph to see if more RAM is warranted. A green graph indicates all is well. Yellow or red graphics indicate the RAM may be insufficient and adding more might help.

If you are having operational problems with your Mac, please describe what you are experiencing and we will do our best to assist.

To avoid us having to play '20 questions' please run an EtreCheck (free) evaluation of your Mac and post the generated report back here in a reply. EtreCheck is a safe and highly regarded utility from a trusted developer and respected ASC contributor. The report it generates will not include any personal info. It simply gathers specifics about hardware performance and installed software that might be in conflict with the OS.

Please navigate to EtreCheck.com to download the utility. Be sure to Allow Full Disk Access when you install the app. Once you’ve run the app and created your report please post it with your reply to this message. 

Please note you must upload the full report. To see how, please click >  How to use Add Text when posting… EtreCheck Report.

We’ll use your EtreCheck report to look for the things that may be causing your problem and advise how to correct them.