use the admin menu, locate the account and delete it
if you do not know account name, but player name, to get account name use this then "props" the palyer for the account name
[global interface where playermobile name = "Name In Quotes with Caps correct"
or for partial name
[global interface where playermobile name contains "Part of Name In Quotes with Caps correct"
if you mean individual character on an account, that is not as easy to do, some one fould a way to do it in game, but it did cause reprcussions
best way is to save server, close it down, open the accounts.xml in notepad, find the account, remove the player from that list, save restart shard, the player is no longer attached to an account and can not be accessed
then can probably delete using other methods
this still may have reprocussions on things
best way is to set it up do characters can be deleted after 1 day or so from being created
thange the persons password (let them know of new password) log on their account and delete the character