Loosen the chuck all the way (or at least enough to get a Phillips #3 screwdriver in the jaws.)

You may need to use the chuck key to loosen the chuck.

Once the jaws of the chuck are open remove the single Phillips #3 screw at the bottom of the chuck while holding the chuck with the chuck key.

Use a pry tool to remove the old chuck.

Reinstall the Phillips #3 chuck screw.