I take it you are talking about the front ones... not an easy job really
If you want to do a proper job, you need to take the calipers off - which is bloody hard with the engine and gearbox on the car, change the seals and o rings, and then re-install them , which is harder due to the handbrake cable !
If you want to do a quick release job and pray they will start working on their own:
Have someone pull the handbrake up and down for you while you watch the caliper's handbrake lever movement. If one of them doesnt move, help it with a screwdriver.
If both of them move and work then its the outter side pistons that are jammed, and you can again help push the pads out with a screw driver.
There are some adjusters for both pistons on each caliper.
The inner ones you can move closer and further away from the disc with a number 10 wrench.
For the outer ones, there is a black plastic cover on the side - number 17 - then loosen just a bit the inner nut - number 17 again, and move the piston in or out with an allen key.
There is a very sensitive o ring in that adjuster, so be sure to hold it tight with the allen key and lock it with the 17 when you are done, otherwise they will start to leak.
You can't undo the lock nut very much as there should be a secure pin there holding it forward.
If you need to take them off.... best of luck mate
No seriously, if you do need to take them off, you need a lot of patience and extra caution not to damage any threads or bolts, otherwise they will never come off with the engine in.