I already have Mojave on my early 2011 MBP. How can I update to Catalina?

I updated my unsupported 2011 MBP a few months ago to Mojave. I know I can't just update the OS through the app store. I've done some searching, but I can't seem to find a definitive guide to updating an already hacked Mojave to Catalina.

Can anyone link one for me, please? Thanks!