Go to System> Tools>Category Editor
On the drop down list find User Role
Anything in red can be renamed.
To add in a role select a blank space or look for User Defined.
Double click onto the field and type in the role which is required, then tick the box at the side. When prompted to replace, click Yes.
Click Save.
Close down Live and then go back to System>User and find your user on the drop down list who requires the new role.
Change the role, click Save.