Need some Advice on New To me Build

Parts I currently have:
Rx580 8gb
Ryzen 5 3600
Asrock B550M-C
Nothing for ram
Cooler Master 212

So 2 questions.

Which memory speed is best for my current specs ? AMD favors speed over size right? This is my first ever amd build, I’ve always been used to intel .

Also , for the cooler master 212, it currently have a intel 1700 socket adapter on it but I was given a AM4 adapter, which is the metal apart that attaches to the board but not sure how Im supposed to take the old one off or put the new one on.