Need Help Removing Brake Switch

I have a 1999 Chevy Tahoe (1998 body style) and I have been trying to change my brake switch since I have not brake lights. The problem is I can't figure out how to remove the retaining clip that holds the switch on to the bolt. I don't want to destroy it trying to figure the thing out but I am stumped. Can anyone help me with this?

I believe I used a flat head screwdrive. Or a fine point.