My daily PC is an i5-3570k and it’s very quick in Kubuntu (that’s Ubuntu with KDE as a graphical environment). I think I have “only” 8 GB RAM and it’s quite enough for my use.

If you’re really not sure and don’t want to break anything, I’d suggest installing some different OSes in virtual machines and try on that first. That might be a learning curve by itself, but you won’t take your computer as hostage for your beginner’s errors.

There are more user friendly OSes than others. I’d go with a Ubuntu or *buntu flavor just for the fact that there’s a lot of beginner friendly websites, tutorials and forums.