i've taken the caliper off and sand papered it and greased it so now i have to pump the brakes for the piston to extend all the way out before it wouldn't move should i just replace the caliper or can i fix it
If it isn't leaking around the seals then maybe you have air in the lines and just need to bleed them. If the bike sat a long time then check to see if the brake line has gone soft.
Master cylinder may need attention as well. Brake fluid is hydroscopic, meaning it absorbs moisture. This water content is capable of corroding the bores, pistons and seals of the braking system. If the brake fluid was not changed at least yearly on this bike there may be trouble lurking that only a complete dis-assembly will reveal. Condition of the components will determine if a rebuild kit or complete new bit will remedy your trouble.
