Once you have the screwdrivers inserted pull on one, and push on the other.
Then reverse the push/pull.
Once you have loosened the bushing take your hammer (or whatever you choose to push the bushing out) and shove on the center of the bushing.
We have found a strong steady push works best instead of small shoves.
Do this for both ends of the mount.
Alternate technique 1
Use a press to press the bushings out. By far this is the easiest way, but not everyone has a press.
Alternate technique 2
Take a big socket and put it on the ground.
Put bushing over socket
Stomp on mount next to bushing
Bushing should pop out and bounce around the garage
Laugh as it bounces around
Repeat for other side