If you are referring to the withholding reported on your tax forms, you may edit those forms in the software. For example, withholding on a W-2 is reported in box 2. Under Wages & Income, click Edit/Add next to Job (W-2). You can then click Edit next to the W-2 and make the adjustments.
If you need to make changes to the withholding in your payroll, you will need to contact your HR Department and complete a new W-4 form. This form will change your withholding going forward. You cannot change withholding from past pay periods.
About Form W-4