In Individual Time Entry, change the Template drop down menu in the middle right to "ALL".
Scroll down until you see deductions on your left and taxes on your right.
Click the box next to the deduction you wish to stop. If you want to override the amount, click Block and then enter in the appropriate amount.
Please keep in mind that any changes made in Individual Time Entry will apply only to that specific check. If you need to make permanent changes to employee taxes or deductions, go to Employee Management > Employee Pay.