how do you change peoples usernames without owning the site

you can't.

I swear people think with name vbHACKERS this site assists in breaking into others vBulletins. When in actuality that's not what hacker is in any way. Even somebody hacking into your computer isn't technically hacking, it's cracking.

Cracker (computing), a person who engages in illegal system cracking or software cracking, circumventing computer security systems; also known as a black hat hacker

A hacker is a person who creates and modifies computer software and computer hardware, including computer programming.