OS update from Yosemite to...?

So I've had a mid 2012 macbook pro for ages that came with Yosemite 10.10.5 installed. Right now I am having trouble using everything, it is extra slow and even chrome/mozilla updates are no longer supported. I don't have money to splurge on a new device and I will soon need this macbook to work on some projects at my job (nothing crazy, just very light video-editing).
Which OS should I upgrade my macbook to? Would that be worth it or since the mac is old I will have pretty much the same problems? What are the steps I need to follow in the process of upgrading? Please explain it as you would to a 6 year old, I literally have no clue lmaoooo thanks to whoever will reply!!