

You shouldn’t need to download any graphics drivers, Ubuntu (and pretty much every other distribution) ships with the open-source AMD driver stack by default, which are significantly better than and less hassle than the proprietary drivers for pretty much all purposes. If you’re getting video out it’s almost certainly already using the internal GPU, but if you’re unsure you can open a terminal and run sudo apt install mesa-utils
and then glxinfo -B
to double-check what is being used for rendering.
Framerate above 20 in what with what settings? That’s kinda key information :P