doddle mate,
just tap out the pins, catch the spring clip and pull out the old 'uns. clean up the pins so they slide in nicely..
then copper slip the new pads (back) and ease the pistons out with a screwdriver and pop the new pads in making sure not to get copper slip all over the place, especially the disks..
you might want to take out some brake fluid from the top up bottle if the pads are heavily worn.
have fun,
/Steve