Depends on the condition of your brake cylinders mate, if they are dirty clean them first then I'd use a piece of wood and push it between the old pads (sometimes this is hard and sometimes not)
noob question (im an electrical engineer ) how would one clean his brake cylinders?
sorry brake pistons,
* take out the brake pads, stick a piece of wood through the caliper (so you can push the cylinders back later)
* use the brake fluid to dampen a cloth
* carefully press the brake ***NOT TO MUCH, just a little bit so you can see a clean surface on the cylinders
* clean around the cylinder with the cloth, if that cleans it use some brake fluid and lubricate the cylinder before you push it back in with the WOOD, DONT harm the pistons.
* if above didnt clean it use a VERY fine sandpaper to get all the dirt off.
Below is a pic that shows how to use the wood: