windshield wiper adjustment

My windshield wipers are off placement. They are two high when they turned off and when they are on they wipe over the outside molding on the driver side. how do i fix this? i tried taking off that cover at the base and losing the nut, adjustinging them, and retightening them but it didn't last. do i have to take the nut al the way off or what? thanks for help
blake