I have a MacBook Pro (Retina, 13-inch, Mid 2014) running version 10.10.5 (14F2511) and can't update my OS.

I got this computer as a gift from my mother-in-law a few months ago and have been using it since. However, every time I open Chrome (or really any browser) it tells me that I am outdated. So I have tried updating my computer, but it doesn't seem like its working...

I've gone to this link (How to download and install macOS - Apple Support) after a few hours of searching online how to update my computer. However, whenever I try to update in the app store, it tells me that my password for my Apple account is incorrect, even though I can sign in just fine using that same password other places (even in the browser on the same computer).

So then I tried downloading the .dmg directly. I run the install program and nothing. I still have 10.10.5 as my version whenever I open my "About this Mac". So I don't understand what to do.

I've tried installing 10.11, 10.12, and even tried 10.13, but as soon as it says "successfully installed" nothing has actually changed and my computer is still at the same version.

I also tried restarting my computer to see if that was the issue, but still no changes. If someone could help me with this, I would greatly appreciate it, thank you!