Removing Locks

Hi,

currently i need to change default desktop via link irj/servlet/prt/portal/prtroot/pcd!3aportal_content!2fadministrator!2fsystem_admin!2fsystem_admin_role!2fcom.sap.portal.system_admin_ws!2fcom.sap.portal.themes!2fcom.sap.portal.portalDisplayRules

but portal says that the object is locked by user xxx. How can i remove lock in this situation?