Bleach

First of all you should use some bleach directly on the mold to help you wash it off. Get a little bleach on the rough side of a sponge with some water and then scrub hard against the area being careful not to damage the paint and not to get any in your eye if you're scrubbing it off of the ceiling. You can also get products that are designed specifically as mold removal products and these of course will help you as well.

Repaint

Just scrubbing the mold may still leave a darkish patch where the mold was or residual mold spores. A great way to get your property looking really good then is to then paint over the patch with a new lick of paint which will make it look vibrant and colorful again. Don't make the mistake of painting only over the moldy patches though - you'll need to repaint the whole wall or ceiling or you will risk leaving uneven patches that are a warning sign to potential buyers. Of course you shouldn't just paint over your mold, and you should make sure to deal with the problem before you try to sell your property.

Check the Sneaky Bits

Mold hides in all sorts of places so don't just do the obvious walls. Check behind furniture and radiators and look inside cupboards and wardrobes too which can often get moist.

Reduce Moisture

In general you should aim to reduce moisture in your rooms or the mold will simply return. To do this you should try to let more air in to circulate and that means opening windows and getting an extractor fan or a dehumidifier installed in your bathroom. If you don't already have double glazing then this is a very smart purchase that you should certainly make as soon as possible to help keep the cold and moisture out of your rooms.

You should also be more vigilant in general to create as minimal moisture as possible, which means for instance drying your clothes outside not inside, avoiding letting water stand in the bath or kettle, and keeping your heating on when it starts to get cool.