Just a quick fix. If your gpu heat sink is dirty, it will throttle down causing fps issues. Blow your computer out focusing on the cpu heat sink and your gpu heat sinks and fans. Use an air compressor. Not one of those can of compressed air.
Also, go to AMD's website and download updated drivers. Your video card isnt that great for gaming so you want to make sure your ingame setting arent too agressive. For starters, turn off bloom and anti-aliasing. turn off shadows and turn down all your setting to low. go from there and see how it plays.