admin rights 'removed'?

hello. I've been doind a huge mistake while configuring my xwiki two days ago and it seems that i removed some admin rights. While i can log in using the standard xwiki admin account, i can't modify the xwiki.preferences, it says that "You are not allowed to view this document or perform this action. " If i did what i think -that is, removing my own admin rights- how may i bring them back? Any way through the database? Thanks a lot.