Ok just found out piston was seized and that the left hand side is really tight now to the disc and wont let me move it to get the pad in, so how do i take to caliper off?
First thing is to free the pistons, the one stuck out is probably slightly on the p**s, If so then you need to take the caliper off the bike, ie wheel out etc, once you have the caliper in your hand, pump the rear break pedal, the in piston will move outwards, if the out piston does not move, put a small block of wood between the moving piston & the caliper face so that when you pump the brake pedal it can not move, doing this should free the stuck out piston.
Once that piston moves ok and has pumped out showing nice clean piston body, block that one & re pump till the other piston shows clean piston body.
Now you need to clean the pistons & the caliper body, it is best to have taken the sliding part of the caliper off, clean with soapy water & a toothbrush, you can use brake cleaner to clean the hard to move crud from the caliper, to clean the pistons use nylon box banding, the stuff they bind box`s with just puy it round the piston & use a see sawing motion, i find WD40 or simalar is ideal to help get crud off the pston.
Clean the sliding caliper pins with emery cloth if coroded, put plenty of grease into the slider rubber boots.
spray the caliper with silicon spray before you put the pads back in, to get the pistons back into the caliper, remove the brake fluid resevoir lid, get a pair of adjustable plumbers nut pliers, as they will open out wide, protect the caliper body & piston with a bit of cloth & gently squeese the piston back into the caliper, when both have beeen done put the sliding part ao the caliper back on, put in your new pads, making sure to put copper grease onto the backs of the pads & the pin that holds the pads on, put back onto the bike, put the rear wheel back in, torque up to the correct torque for rear wheel axle nut pump your brake lever to bring the pads into play & away you go.