Bridge pins usually stick because the ball end is wedged against the pin or the bridge plate. The tuned-up string holds them there, so the first step is always to detune it.
Step by step:
- Detune the string until it is completely slack.
- Push the string toward the bridge so the ball end drops away from the pin.
- Lift the pin with a bridge pin puller or string winder notch, pulling straight up.
- If it still won't move, reach through the soundhole and press up gently on the underside of the pin from inside.
- Protect the bridge with a cloth if you're using any tool for leverage.
When fitting new strings, put the ball end in the hole, push the pin in, and pull the string up gently until the ball end seats against the bridge plate. Then tune. A pin that rises as you tune means the ball end hasn't seated.
If pins are cracked, loose in their holes or hard to remove every time, have a technician look at them.