To remove a user from a group select “Manage > Users and groups” from the top menu and click on that learner from the list to access their profile page.

On the user’s profile page, in their details panel click the bin icon next to the name of the relevant group you would like to remove them from.

The user will no longer be able to see the courses available to the group within the Course Library (Assignment related courses are unaffected). However owners will still be able to view results from previous attempts.