Updating OS X

I decided to update from El Capitan to Big Sur, Since my internet is really slow i waited 6 hours for it to install. It finally finished and it restarted my computer, I logged in and I went to "About This Mac" expecting to be on the version i just downloaded but I was still on El Capitan so I tried downloading Catalina but the same thing happened again, (Quick note is that it would download but it would not install after rebooting my PC.) I was wondering if anyone knows why this is. Thank you in advanced.

submitted by /u/Organic_Fennel7826
[link] [comments]