Before you embark on changing a light bulb, there must be a reason that led you to that, and this could be that the bulb is no longer working or you need to get a fancier one. Whichever the reason, ensure that the switch is turned off before doing anything. If the bulb was on, it is probably hot so let it cool down.
Remove the bulb that needs changing, and if it’s burnt, dispose it off. Fix the new bulb carefully without using a lot of force. Finally, you need to switch on the lights to ensure that it’s working since the results will tell you whether you need to fix a new another one or not.