Only the Account Owner or Administrator can remove Users from the account.
Step 1: Begin by opening the Settings Dropdown and clicking Account.
Step 2: Find the user to remove, and click the trash icon to the right of their name.
This does not completely remove the user. It will archive them and block them from logging into that account again. You can un-archive someone by clicking the lightened Archive icon next to their name.
If you wish to update your billing, contact Support at email@example.com or at 855-427-4848. You will continue to be billed for the archived user until you contact support.