(Only on sims free play) I would recommend being the sim you want to rename, and then tap on the sim you want to rename, then near the right top corner there should be a red circle sign, click that and then it will ask you if you want to move the sim out of town, click yes and then go to the town map and move a new sim in the house by clicking the icon on the house, then you can name it something different, hope this was useful!