Can i add RAM to iMac Retina 4K, 21.5-inch, 2017

You were advised correctly. In that model, iMac18,2, the memory can't be user upgraded. You're locked in to what you've ordered. You might find an Authorized Apple Service Provider who will add additional RAM to the iMac but it will void the warranty. Only the 27" models can have the memory user upgraded.

If the lack of memory makes the iMac unusable for your purposes you may have to sell it and buy a 27" model where you an upgraded the memory your self from Crucial.com or MacSales.com at about 1/2 the price that Apple charges.

If you do sell the iMac be sure to prepare it according to this Apple document: What to do before you sell or give away your Mac - Apple Support

Yes, although it's possible for an owner to upgrade the RAM because the RAM is not soldered on, it will void the warranty if not done by a AASP. FWIW, not all AASPs will upgrade them. You have to ask. I'm lucky to have one locally.

Welcome!

The simple answer is "no." The iMac 21.5-inch case is not intended to be opened.

The complicated answer is that if you are skilled at opening and resealing computer cases that are not designed to be opened and feel OK about removing ALL the internal components to get to the two deeply buried RAM slots, then "maybe." I take computers apart fairly regularly and would not undertake it. Due to the cost of the resealing supplies and special tools, a 16GB upgrade kit for your model costs twice that of a 16GB kit for a 27-inch iMac to which a user can add RAM by simply opening a little access panel. The seller of the upgrade kit also provides this caveat right on the selling page:

Doesn't give me the Warm Fuzzies about the process.

You can do two things:

1) Sell the computer and apply the proceeds to one with 16GB RAM (the most Apple installs in that model), or a 27-inch model--their RAM is user-serviceable.

or

2) Let us see if we can make the 8GB RAM you now have work better.

For Item 2, we need two things:

a) You wrote: "...I don't have enough RAM for my workload." Please tell us what software your workload requires. That will help.

b) Please post a snapshot of your system configuration so we can look for known software conflicts that can reduce RAM available to the apps that earn you money.

Step "b" is not hard. Fortunately there is a safe and secure way to do that.

A respected and long-serving member of these communities has created a simple utility that will take that "snapshot" of your configuration without revealing any sensitive information about you and your computer. It only runs when you tell it to, not in the background, and therefore creates no performance penalties. It is Etrecheck, and is available here:

http://etrecheck.com/

Run it and, when its results display, select "Report" from the left-hand pane (scroll down), then click Etrecheck's "Share Report" icon followed by "Copy Report" from the resulting dropdown. Paste the entire report into a response to your own thread here. It will often allow us to quickly identify or eliminate software as the problem.

FWIW, I wanted to check on this so I emailed my local AASP and here is his reply.

Hi. If the upgrade is done by the Apple Store or an AASP such as ourselves it does not void the warranty.

Assuming he's not lying apparently the OP can in fact have his RAM upgraded without voiding the warranty. Although I don't think most Apple Stores will do upgrades.

That's good to know. I guess it's the owner doing the upgrade that will void the warranty. Might be a bit costly but maybe worth it in the long run.

FWIW, an Apple Authorized Service Provider can upgrade the RAM.

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