I need help changing the account used to authorize things!

Whenever i go to sync anything at all from my computer to my ipod it says i need to authorize it first, so of coarse I click authorize but the problem is that it only wants to let me authorize it from my friends acount becuase she used to get everything on my ipod for me. And unless i get the password for her acount i cant get any new apps, songs or updates on my ipod. Even thought i am signed in on my acount it says i still need authorization for my friends acount. Is there any way i can delete her acount from my ipods memory or whatever so i dont need that acounts authorization? And ive tried to go to Store> Veiw my acount, but it wont let me edit the: Computer Authorisations?? Please help!