The best way to ensure what the optimal tax withholding will be for you is to use the IRS "Tax Withholding Estimator" tool, https://apps.irs.gov/app/tax-withholding-estimator, to calculate your taxes owed.
After doing this, go to https://www.irs.gov/pub/irs-pdf/fw4.pdf, and prepare your W4s. You may want to consider making additional tax withholding in Step 4(c) of the W4. You will then take the W4s and go to your employer's site and make the changes accordingly.
