Change to what? You mean take down the old and put up a new one? If you need to ask you probably shouldn't be doing it, but have a look at the Wiki anyway.
Best advice as a DIY'er i can give is to before starting take a picture of what it looks like at the moment with the cover removed and the power off now normally its just a undo the two screws holding the cable and then remove the old fitting, attach new fitting to the ceiling and reconnect the wires and job done
for a reasonable diyer i'd say 15-20 mins including the reassuring the mrs that you wont blow up the planet and tidying up any possible damage to the ceiling
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local