Once you contract vampirism and before the 3 days pass where the disease becomes permanent, you have two options of curing it. The first one is to use any common disease-curing potion and the second is using the Shrine to Talos outside Whiterun or Dragonsreach. If you've contracted the disease and it has become permanent, there is only one way to cure it. First, make sure that you're not a stage 4 vampire, as you will be attacked by any NPC. There's a tavern due south of Whiterun, where there's someone sleeping upstairs after 2AM; just make sure you sneak by the two guards who patrol the area. To actually cure the permanent vampirism, go to any inn keeper or bartender and ask about rumors. This should lead you to Falion in Morthal; Morthal is located east of Fort Snowhawk. Talk to him and he'll mention that you need a Black Soul Gem (you can buy one from him), but you need to fill it. To do that, you need the Soul Trap spell and use it on a human, then kill that human; it doesn't matter which human you use. If you don't have the spell, you can buy it from any magic vendor; if you can't use the spell, then buy a Soul Trap scroll. Whenever you have the Black Soul Gem filled up, go back to Falion and he'll cure you of your vampirism.