To correct or change your exemptions used to calculate your W-2, you have to file a new Form W-4, Tax Withholding and Estimated Tax. This includes a worksheet to prepare the form, and IRS ...

You can correct a W-4 form anytime, but you are not required to file one yearly. If you are happy with your current tax withholding, you can leave your current Form W-4 in effect with your employer.