Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
Im not sure why the other company told you your computer had all kinds of issues.. ( If you paid them, I would consider calling your bank or ceredit card and disputing the charge )
With that being said, all you need to do is go into your yahoo profile and make the needed changes there.. Would you like me to quickly connect and show you how to do that on screen? ( Dont worry, Im not going to try and sell you some software or claim you have some horrendous computer issue, as this is a matter of changing your yahoo profile settings and name, nothing else )
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.