Once you have fully turned into a Vampire (resting after three days from contracting the Porphyric Hemophilia disease), you can only cure Vampirism by completing the lengthy 'Vampire Cure' quest, or finding the Font of Renewal as part of the 'Deepscorn Hollow' quest in the Vile Lair DLC (this DLC is thankfully included in the Remaster).

There are three methods to curing vampirism in Oblivion Remastered, which are as follows: Cure it as a disease in the first 72 hours when it's still Prophyric Hemophilia. Find and use the Font of Renewal in Deepscorn Hollow. Complete the Vampire Cure quest with the Witch Melisande.

To cure vampirism in Oblivion, you need to travel to the Arcane University in the Imperial City and accept the "Vampire Cure" quest from Raminus Polus. Once you've become a vampire, the "Cure Vampirism" dialogue option will appear when talking to healers and other relevant NPCs. They'll all point you to Raminus Polus, kicking off the quest.