go to pacommunity.co.uk, log in with your in-game nick and password, click on your nickname on the top right corner, and click 'view profile', and below your nickname, there's a button named 'edit profile', click on that, and type the new name you'd like to use on the first box and click save profile. You'll have to wait until a PAC admin logs in and accepts the changes. This might take up to a few minutes to days. Hope this helps.
VC-MP: 
