Need some help with getting stock rom

[Roni96]

So I bought used htc one m7 that has viperone 7.0.1 rom installed in it. I don't want that so how can I get rid of it and install normal stock rom? I tried to watch some videos and every time I should type "adb something..." On cmd it says adb is not right or something like that. Also when I'm fastboot it says "tampered" what does that mean? And also my phone has s-on and its unlocked. I also tried to update my htc drivers but that didn't work either. When I was unzipping the file it said "this file is too long" and I couldn't finish it. What can I do now?

 

[Roni96]

I just spend 6 hours on computer and i couldn't get anything to work... Is this what android is like? I've really started to think that this was a bad decision