How can I install chrome extensions on an out of date chromebook?

I bought a refurbished Chromebook on Amazon and didn't know it couldn't be updated. That part isn't mentioned anywhere in the sellers description. I cannot install any chrome extensions because Chrome is out of date. (It wont even update chrome browser let alone the system) My Chromebook is useless to me if I cannot get some of the extensions I need. I read somewhere that Chrome extensions can be installed without the chrome web store. I've tried figuring something out on my own, but I'm so computer illiterate it's not even funny. **Can install Chrome extensions from somewhere other than Chrome Store?**