Contacts can be removed from a group in bulk from the Contacts module.
To do so, first get your required contacts into a selection. To do this you can perform a yellow box search, saved search or any other way of selecting the contacts.
Once this is completed, follow the steps below:
Click Select All on the left side of the page.
Click the Group options which will appear at the top of the screen.
Click Remove from Group.
Select the group.