You can not delete key groups
.

But you can delete groups that you add.

the forum' modules deals with knows group numbers, for example 1 for the admin, 7 for guests, and so on. But you can edit the group and choose enable member hide and not to be shown in the groups list on main page.

اقتبـاس ،، I changed name of General supervisor to "Administrator" but I have pBBoard shows me General supervisionin profile.

Control Panel » Members » Edit : Admin
title member = Administrator

In PBB you can use custom title for the members.