My GTX-1080 is getting a little long in the tooth, I'm thinking of going all AMD on my Linux Mint gaming rig here, but…is there anything I need to do or install or uninstall to switch to an AMD card from an Nvidia one?
I've never done this before on a Linux system; I've got my Intel/Radeon laptop, and my Ryzen/GeForce desktop and that's most of my Linux experience.
I thought that as long as the kernel is new enough, the Radeon driver should already be in the kernel
Yes, it works this way. An additional driver is not needed for AMD.