most twist quarter of a turn counter clockwise.some are fixed with a center nut disguised as a decorative screw off attachment .since you have described yours as having a slot for a flat headed screwdriver,I can only assume this is to release the shade from the housing,ensure power is switched off,insert flat screwdriver into the locator and using minimum pressure push the release tab in and try and twist or pull the shade.check otherside of the shade for a similar tab release slot.
mech monster, November 2011
