Wikipedia:Arbitration Committee/Directory/Conduct/Administrator
Administrator dispute
Please see Wikipedia:Administrators § Grievances for information about how to deal with administrator misconduct. Talking to the admin is the first step. If that is unsuccessful, you should utilize one of the forums which review admin actions.
If all of that has been attempted unsuccessfully, and you are still certain that the administrator needs to be desysopped, you may file a case request.