A. SAFETY FIRST! I would definitely recommend turning off the circuit breaker that controls the circuit for those lights. If everything is wired correctly, simply having the light switch off is enough, but if the wiring was connected "backwards" you could conceivably complete the circuit from the fixture through yourself to the ground, and that would not be a fun experience.

If the broken bulbs still have the filament portion intact (the glass and wire doodad that protrudes from the center), I have been successful in carefully holding that between thumb and forefinger and gently unscrewing the base from the fixture. Be very careful if you try this, as the glass that encloses the filament might shatter and cut your fingers.

If all that is left in the fixture is the metal that screws into the base, I would suggest using a pair of needle-nose pliers to take hold of one edge of the metal, and with a bit of wiggling you should be able to move it counter-clockwise until you get it completely unscrewed. If you don't have any needle-nose pliers in your toolbox, you should be able to find some inexpensive ones at any hardware or discount store for a few dollars. You want a fairly small pair for this job. You will be able to use them for many other small projects like fixing the chain on a necklace, or holding something in place that is too small to grasp with your fingers.

I have never heard of the potato trick. I can see where it might work, but I think I would go with the pliers. Remember that a potato is full of water and I'm sure that it would be happy to conduct electricity from the fixture to you if you don't have the power turned off at the breaker panel, so if you try it with a potato or my way, POWER OFF FIRST!