Spray with some liquid wrench, wait, use half inch ratchet/sockets/extension, try to tighten a wee bit before loosening. Cover your tank and front fender from bar/tool drop.
When reinstalling use antiseize.
All good advice.
When I removed the aftermarket risers on my bike that the PO installed one side came off like clock work and the other gaulled after the first half-turn. A royal PITA but it did come off eventually. Did pretty much what Jess said to do.
I wasn't going to re-use these risers so it didn't matter to me if the bolt would've broke off or if it stripped out all the way which either one of these methods wouldn've been better for me. Unfortunately it unscrewed ALL the way.