you follow this quest http://www.uesp.net/wiki/Skyrim:Rising_at_Dawn
Spoiler all you need to do is to talk to an innkeeper about vampires and they will leed you to the cure quest, but here's a warning, once you are cured there's no way back
Not true. You can contract http://www.uesp.net/wiki/Skyrim:Sanguinare_Vampiris again after you've cured your vampirism. You can contract and cure vampirism as many times as you want. Lycanthropy is a different story and even that has been changed so that, if you become a Vampire Lord, you can change back to a wearwolf. However, under normal circumstances, if you cure lycanthropy by any means other than becoming a Vampire Lord, you cannot contract it again.