Step 1: Click on your initials located on the left corner of the screen, select " Settings and Billing":
Step 2: On Billing > Subscription, adjust the amount of active seats:
Step 3: Next under Company settings> User Management, check next to the user's email address, you will see that the user is still "Active?":
Step 4: Next to the user's email address that you want to remove, toggle this button under "Active?" off: