The Curse status ailment is one of the more annoying ones in the game, since if you do get cursed, it halves your maximum HP (some have said multiple suffering of curse stacks, but some are saying you can only get cursed once and the effect doesn't stack). One of the easiest ways to get cursed is by the Basilisks (commonly known as frogs) in The Depths, but there are other enemies who can curse you. To remove Curse from your character, you will need a Purging Stone and there are a few ways to obtain one. You can trade Snuggly the Crow a cracked red eye orb for 2 stones. Also, the giant clam enemies in Ash Lake and Crystal Cave drop them. The easiest way to get Purging Stones is to buy them, either from Oswald the Carim in Undead Burg (3,000 souls each) after defeating the Gargoyles, or from the Undead Female Merchant in Firelink Shrine (6,000 souls each).