How to recover my lost/forgotten password in my Linux terminal?

The first problem I have is that I'm a low tech elderly guy. I've received recent updates for the first time in years. I currently use 14.04 & wanted to update to 16.04 but I now understand you've already on 20 or 21 & I have never received any notice of any updates until a few weeks ago. But I can't update because I can't get into the terminal as I lost/forgotten my password. I've tried many web-sites including webmaster@ubuntu.com & many have offered free assistance but, I've tried everything & cannot get into my terminal. Is there a way to recover my terminal password so I can follow updates?