Now to remove the pads, and put in new ones you need to push the pistons back into the caliper.
There are a few techniques to doing this, but there's some tips.
1) Do one pad at a time. In other words, compress one side, put new pad in place, and then do the other side. If you do both then you'll just be fighting the pistons on the opposite side because as you push one side in, the other side will push out.
2) When compressing the pistons you can approach the fluid two ways.
a) Leave it be, but when doing this do remove the cap from the brake fluid reservoir.
b) You can crack open one of the bleeders (this will require you bleeding the brakes - upcoming paper)
First is the pliers technique:
Use some pliers to push back the pistons by clamping on the caliper and the backing plate. Do this carefully so you don't chip the finish.
Second is the wedge technique.
Jam a screwdriver between the pad and the rotor and push the pistons in.
Third is the pad lever technique.
We failed to get a pic of this.
Wiggle a pad out part way with the pad material facing the rotor. Use it as a lever to push the pistons back in.
Fourth is the tool technique.
There are some special tools for doing this for both monoblock and slider style calipers. We've never needed them, but if you have them then use them.