These actions can only be performed by the Primary Account Admin user (with the Account Admin level users also able to perform these actions for certain user types on the account e.g. Team Members. Account Admins cannot manage role permissions of other Admin users; only the Primary Account Admin user can do this).
Log into your account, navigate to the Business Account Settings section of the application.
Navigate to the Your User List sub tab.
You will see a list of the users associated with your Business Account. When you hover over the users in the list, you will see an edit pop up in the Status column where you will be able to change the Status of the user - including deleting or deactivating the user.
NOTE: you cannot currently permanently delete an onboarded a user from your business account. If you want to remove a team member from your account you must use the "Inactive" status. This is because your Business Account must keep a record of the activity, programs and actions of any user, current or past.