How do I increase RAM on iMac?

MacTracker says that an iMac (Retina 4K, 21.5-inch, 2019) can take up to 32 GB of RAM (official limit) or 64 GB (actual limit). But the RAM slots are sealed inside. As the others said, this is a job for a repair shop.

Before upgrading RAM, you might want to check if you need it. If you run Activity Monitor with the Memory tab selected while you are carrying out normal tasks, what does the Memory Tab indicate?

There are two things you are looking for:

• The color coding on the Memory Pressure graph. Green means you have enough RAM for what you are doing. Yellow means RAM is marginal. Red means you don't have enough, and that is hurting performance.
• Swap Used. A high Swap Used figure could also be a sign that you need more RAM.

If those things are fine, then RAM probably is not your issue.

Memory is not removable by users on iMac (21.5-inch, Late 2012), iMac (21.5-inch, Late 2013), iMac (21.5-inch, Mid 2014), iMac (21.5-inch, 2017), iMac (Retina 4K, 21.5-inch, 2017), and iMac (Retina 4K, 21.5-inch, 2019).

If you’d like to upgrade the memory in one of these models, an Apple Authorized Service Provider can help. Before you schedule an appointment, confirm that the specific Apple Authorized Service Provider offers memory upgrade services.

Accessing the RAM slots requires the nearly complete gutting of a computer that Apple did not design to be upgraded. As 6x6 pointd out, some Apple Authorized Service Providers will not attempt that work.

If your 21.5 inch iMac is slow, it is far more likely a storage problem than RAM. For base models Apple used mechanical hard drives that were slow from Day One. Here's a quick quiz:

• Is your Mac slow to boot up?
• Are apps, especially big ones like Office, slow to launch?
• Once launched, do those same apps seem to run at acceptable speed?

Three "yes" answers stongly suggest a slow mech hard drive, not a RAM issue.

Our diagnostics are limited in this user-to-user setting where we can neither see nor touch your computer. There is effective help though: a snapshot of your software configuration. Fortunately there is a safe, secure way to show that to us so we don't end up playing a protracted game of "20 Questions" that could go on for days.

We can quickly and within the confines of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software conflicts, and RAM usage. Etrecheck is the development of a long-serving and trusted contributor here expressly for displaying information in these forums to help us help you. It will not reveal any personal or secure information. Even with its security protection, EtreCheck is comprehensive enough for us to see and recommend at-home fixes from one posting.

As the report often contains subtle clues not apparent to the casual computer user, the report is designed to be posted here where we old greybreards have interpreted thousands of such reports. Please this excellent user tip on posting long text reports like EtreCheck's.

How to use the Add Text Feature When Post… - Apple Community

People aren't meant to do that themselves. Contact an authorized Apple service provider.

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Allan Jones wrote:

If your 21.5 inch iMac is slow, it is far more likely a storage• problem than RAM. For base models Apple used mechanical hard drives that were slow from Day One.

Apple offered a 1 TB Fusion Drive for that iMac – but that drive would also be slow.

It consisted of

• A slow 5400 rpm 2.5" notebook hard drive, joined in software to
• A mere 32 GB of flash (SSD) storage (prime real estate, but not nearly enough of it)

The original 1 TB Fusion Drives had 128 GB of flash storage. As the years went by, and SSDs got cheaper, Apple made the puzzling decision to cut the amount of flash storage in 1 TB Fusion Drives, rather than to increase it.