To delete a local group

To open Computer Management, click Start, and then click Control Panel. Click Performance and Maintenance, click Administrative Tools, and then double-click Computer Management. 

The following built-in groups cannot be deleted:

A deleted group cannot be recovered.

Deleting a local group removes only the group; it does not delete the user accounts and global groups that were members of that group.

If you delete a group and then create another group with the same group name, you must set new permissions for the new group; it will not inherit the permissions that were granted to the old group.

Local Users and Groups overview

Add a user to a group

Create a new local group

Delete a local group