All Administrators have the capability to remove a User from any Groups as well as removing them entirely from smrtPhone.
To remove a user:
Go to the Admin panel (≡) from the left navigation
Click on Users from the menu
Find the User you wish to remove
Click the Trash Can icon / Remove User button to the right of their name
Confirm that you wish to remove them
Note: When you remove a User, it's helpful to double check that all Call Flows and SMS Flows will continue to function as intended. If there were any Call Flows or SMS Flows that named the individual User that is now deleted, you'll need to update those Flows or incoming calls and texts will not be received.