How to upgrade memory in a 2017 iMac 21.5 inch Retina 4K?

While that Mac has two RAM slots, they are sealed in. Opening the Mac to get to them, and resealing it afterwards, is a job best left to professionals.

IMacs can be picky about RAM, so I would suggest getting the RAM upgrade modules only from Other World Computing.

Between the cost of professional installation, the recent spikes in RAM

prices due to an AI company cornering supply, and the need to remove all of your existing RAM, an upgrade could get expensive. So first check if you really need the RAM.

Hi,

Yes, you can upgrade the memory (RAM) in a 2017 21.5-inch Retina 4K iMac, but it is not designed as a user-upgradeable process. It requires removing the screen and disassembling the machine to access the RAM slots, unlike the 27-inch model. Professional installation (Apple Authorized Service Provider) is strongly recommended.

Memory type is 2400MHz DDR4 SO-DIMM.

No. Contact an authorized Apple service provider.

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You've been offered lots of good guidance by our friends here. 👍🏽

I'll simply add that you can use Activity Monitor app to view a graphic display of the memory pressure that your Mac is experiencing. If the memory pressure is green, then RAM is not an issue for whatever you are currently doing with the computer. A little bit yellow suggests you might improve things by reducing the workload as by closing unused apps and such. A red memory pressure graph suggests that yes, the amount of RAM you are currently working with is insufficient.

This is Apple guidance for using the Activity Monitor app:

View memory usage in Activity Monitor on Mac - Apple Support

What kind of App's are you running on the 2017 21.5" iMac..?

If you are only running macOS app's, then it should run fine on 8GB of RAM.

If you are running Microsoft or Pro app's, then you should consider replacing it with a newer more powerful Mac.

see > Help me choose the best Mac