Click the arrow circled below to expand the Taxes section:

Select Tax Withholding:

Select Update Forms in the top right corner:

Select Start:

Select which options you would like to complete:

If you select to change your federal tax withholding elections,  the system will walk you through the steps below, while auto-populating your Form W4 for you along the way:

You will then have the option of submitting your Form W4 changes or you can return to the previous page:

If you selected to change your state withholding as well, the system will then walk you through your state tax withholding election options as well.

You will then have the option of submitting your state tax form changes or you can return to the previous page: