You must have a slot A like me.
You can buy a "goldfinger" device from hardware sites, but don't expect huge speed increases, and budget for a fan that shifts LOTS of air. I bet your Athlon runs hot. I wouldn't expect more than 850 from your 700. In all the goldfinger will cost 2 or 3x as much as a powerful fan so we aren't blessed with the most cost-effective overclocking solution.
Of course the Athlon is deliciously fast anyway, but if you must have the most speed, you have to overclock on Socket A, I think.