To remove a curse in the Sims 3, you will need to find a witch NPC (Non-Playable Character) and ask them to remove it. To find a witch NPC, you will need to travel to the town of Moonlight Falls. Once you are in Moonlight Falls, you can search for the witch NPC by clicking on the Map button in the bottom right corner of the screen and selecting the "Sims" tab. The witch NPC will be marked with a green star icon. Click on the witch NPC and select "Ask to Remove Curse." The witch will then remove the curse for a fee.