Ok,I will explain it once again*sighs*:
1)Go where it says User CP
2)Choose the Edit Profile Option
3)Once u have clicked on that option,u have to go where it says:"Optional Information - All information will be viewable by other forum members",and under that tittle there´s another thing that says :
Custom User
TitleThis is the title that appears beneath your name on your posts. Check the 'Reset' box if you wish to use the the default title for your usergroup and post count.
And that´s the place u can change the name below your username