There are many situations which might require to remove someone from your experience. Maybe a student has dropped out, a mentor switched organisations or a test account needs to be deleted.
To remove someone from the experience, you need to go to the enrolments screen.
There, you can simple delete the enrolment by clicking on the "Bin" icon at the right hand side.
Once the enrolment is deleted, the user won't receive any emails or notifications anymore and will not be able to login to the experience anymore.