How Do I chang the Username for a cuurent Domain

[dataonline]

Dear all,
i have ceated numbers of domains name under 1 plesk account after that i found out that its beter to create a seperate plesk account for one of those domains so how do i accopmlish this task is there any utilities which help make that done ? , and please be noticed that i have created an emails account under this domain using plesk ofcourse