DIY, is highly discouraged for this model! Getting into an iMac is a HUGE P.I.T.A. All of them are literally hair-pulling experiences. I do alot of work on Macs and they can be a harrowing experience. I really wish that they would just stick to their large(ish) tower designs which are very easy to manage for repair and upgrades.
Apple always comes up with these funky designs, which look great, but are always a nut-cracker to repair. I have sliced open more than one finger doing repairs in the past. The greatest designs and easiest to work on are usually the most boring design-wise. It’s always a trade-off.
And their laptops? Fugaddabahddit! Worst experience ever. Unless you actually have the tools, which you have to get from Apple, it’s a nightmare.