Remove the strings.
Unhook the springs in the back, using a pair of needle nosed pliers if necessary.
If it's a knife edge type, it'll now be free to lift out of the body. If it's a six screw type, it'll now be left to flap around.
Undo the six screws. (if necesarry)
Lift out the bridge.
Install the new bridge, ensuring that the six screws aren't so tight that they lift the bridge from the body.
Replace the springs in the back.
These go to eleven...