What form is used to cancel tax withholding

Cancell what tax? Are you wanting to have less taxes taken out of your pay or what are asking?

The amount of income tax withholding on your paycheck is determined by your wage rate, your marital status, and the number of "allowances" that you claimed on your W4. It's possible to claim exemption from income tax witholding, but only if you owed $0 in taxes last year and expect to owe $0 in taxes this year. As for social security - that's a flat tax on the first $106.8K of salary.