You don't need to change your nail polish until it starts getting chipped, which is usually within a week. There's no particular reason for removing it unless you want to change colors for a night out, or if it starts to look ratty. Some women do their nails on a particular day—like Saturday afternoon—just to keep a routine going. But it doesn't really matter.

However, using acetone based remove more than once a week can weaken nails causing them to break more easily.