Circline fluorescent lights operate exactly the same as straight bar fluorescent lights; they just happen to run in a circle. The only major difference is that with Circline lights, you must plug the ballast directly in to the light bulb. This is not necessary with most straight bar fluorescent lighting. Circline bulbs offer more light for less energy than conventional light bulbs, generate less heat, and are considered by many to be more aesthetically pleasing in living situations than industrial bar lighting.
Support the light fixture cover as you remove it. Removal is usually accomplished by either flipping plastic holders away from the edges of the cover or unscrewing screws that held it under tension.
Grasp the ballast plug as close to the Circline fluorescent light bulb as possible, and pull it straight out from the bulb. If the plug is difficult to remove, try wiggling it very gently from side to side as you pull.
Support the Circline fluorescent bulb with one hand as you flip the metal holding rings off the bulb one at a time with the other hand.
Pull the bulb a little further out of the fixture as each holding ring is released. Once it's completely free of the holding rings, place it to the side.
Place a new Circline fluorescent bulb in place, and snap each holding ring into place on the bulb. There are usually three holding rings per Circline bulb.
Plug the ballast plug straight into the new Circline fluorescent light bulb.
Reattach the light fixture cover, making sure to support it with your hand until it's firmly fixed into place, either under tension from screws or with plastic holders flipped back into place.