I am pretty computer-dumb. I am still operating on Mac OS X 10.10.5 MacBook Pro (15-inch, Mid 2012 with Yosemite) and have started to lose functionality - some websites don't open, softwares don't work, etc. due to my outdated browser. When I go to the app store to view available updates, there are none. Months ago I tried to manually update the OS to Catalina (I think) and it completely crashed my computer; I had a smart friend restore it, but it is back to the old OS. How do I get something more functional so I can download new browsers, etc?
I would start first opening this link in safari.
Don’t take the bait in step 4 trying to get you Catalina, You want this next link first...
While it’s downloading check your backup is solid. The upgrade and updates don’t intentionally erase data, but better safe than sorry.
Also, seriously consider an internal SSD if you move to APFS and past High Sierra.