The delete button allows you to delete the selected User Group. You will be taken to a confirmation page prior to the User Group being deleted from the system. The software will detect if there are any current users within the User Group you are trying to delete. If users are detected, you will be prompted to choose another User Group to move those users into prior to the system deleting the selected User Group.

You cannot delete the user group with the internal id of 1. This is a fail safe so you as the admin cannot ultimately "shoot themselves in the foot" and delete all user groups within the system. Doing so would result in an unstable state, and possibly cause the database to be "corrupted". There will always need to be at least one user group in the system.