Inspect your replacement bulb, making sure there is no visible damage, and check its specifications on the side of the packet. Test the bulb in a reliable store before purchasing it.
Turn off the light switch and leave the old 300W halogen bulb alone for a couple of minutes to allow it to cool down. One of the characteristics of large-watt halogen bulbs is that it generates a lot of heat. If the bulb is being replaced on the ceiling, make sure your step stool or ladder is stable before climbing up on it.
Remove the heat guard, if there is one, and set it aside. Push in and twist the old bulb carefully or unscrew it in a counterclockwise direction. Wear gloves to avoid leaving oil prints with your hand.
Carefully insert the new bulb into the fixture in the same manner that you removed it. Make sure the bulb is secure before you let go of it.
Turn on the switch to test whether the bulb is working. If not, switch it back off and return to the bulb. Unscrew it and start over. If the fixture has a spring, it must be pushed in place before screwing in the bulb. Apply moderate pressure on the spring to avoid damaging it. Ensure your bulb is at room temperature during reinstallation.
Replace the heat guard, if there was one. Wrap the old bulb in hard paper to avoid injury from falling on it or breaking it on the floor. Dispose of it in a recycling bin.