Hi,
You may achieve this as an administrator and also by using the Advanced group manager extension.
1. As an administrator, please refer to the following steps:
A. Login to your WordPress Dashboard and click on Users
B. Click on All user >> All User list will appear
C. Select the User you want to remove from the group.
D. Click on Edit
E. Now the User Profile will appear
F. Scroll down and go to User Group(s) option
G. You will see the groups there H. Deselect the group by using Ctrl key + Click
H. Click on Update User to apply changes.
2. Using the Advanced group manager extension administrator or Group manager can remove the user from the group from the front end. For more details on the Advanced group manager extension, please visit https://profilegrid.co/extensions/frontend-group-manager/.