This is probably listed but i couldnt find it and i plan to say it very easy and followable.
1st- A Private sever (either you host it or have database access)
2nd- Get people to join
3rd- Go into your database and locate where the accounts are located
4th- about 50% of people put there retail info
5th- login there account at WorldofWarcraft.com
6th- change pass
7th- enjoy