If you can't figure out how to remove the bulb from one of your track lighting fixtures, it isn't because the manufacturer designed it to be impossible so you'd have to buy a new fixture. On the contrary, these bulbs are easy to remove. These multifaceted reflector bulbs -- MR bulbs for short -- can have a screw base like a conventional bulb, but the ones most commonly used for track lighting have either a two-pin base or a turn-and-lock one.
Replacing an MR16 Bulb
MR16 bulbs have two pins, so to remove one, you have to be able to grip both the bulb and the fixture connection.
Remove the lens from the fixture by gripping one end of the metal clip holding it in place, using a pair of pliers, and pulling that end toward the center of the lens to disengage the clip. Remove the clip, and the lens should fall out into your hand.
Grip the wire in the back of the canister and push it forward; the bulb should come easily out of the front of the fixture. Keep pushing until you can grip the porcelain base into which the bulb is plugged.
Hold the base with one hand and the bulb with the other and wiggle the bulb gently while you pull it. It should come loose with a little effort. Don't force it -- the glass base of the bulb can shatter.
Plug the new bulb into the base; the prongs are interchangeable, so it doesn't matter how you orient the bulb. Push it back into the canister, replace the lens and reset the clip to hold it. Turn the power back on and test the bulb.
Replacing a GU10 Bulb
GU10 bulbs have a twist-lock base. You can tell your fixture uses this type of bulbs because the bulbs aren't covered by a lens.
Place your hands on either side of the canister and press your thumbs against the front of the bulb.
Push the bulb toward the back of the canister while you rotate it counterclockwise as far as it goes -- typically about a quarter turn. Release the bulb, and it should fall out of the canister.
Install the new bulb by fitting the two prongs in the base into the round holes in the base of the canister. Push on the bulb with your thumbs while you turn it clockwise to lock it into place.