Introduction
You can remove Learners from Courses, Tracks, and Paths via the Accounts screen in the Administrative side of your database. You can also remove a Learners Course via the Manage Accounts modal on the Course management screen, and you can expire them from the Course. If the Learner accessed the Course via a Product purchase, you can refund and remove the product that granted the Course, which will also remove them from it. If you just want to refund the Course, you can do this without changing the Learner's enrollment status.
Refunding Learners and Removing them from the Course, Track, or Path
You can refund Learners and Remove them by using the Refund and Remove tool on the Product that was assigned to the Course, Track, or Path. Login to the Administrative side of your database, go to Accounts, and use the Search tools to find the Learner's Account. Find the Product purchase, click the "Refund and Remove" button, click the "Refund Selected Items" button,
Then, complete the Refund screen. This will both refund the purchased Product and un-enroll the Learner from the assigned Course, Track, or Path. 
Refunding Learners without Removing them from the Course, Track, or Path
You can refund Learners by using the Refund Only tool on the purchased Product. The Learner will stay enrolled in the Course, Track, or Path that was assigned to the Product. Login to the Administrative side of your database, go to Accounts, and use the Search tools to find the Learner's Account. Find the Product purchase, click the "Refund Only" button, click the "Refund Selected Items" button.
Then complete the Refund screen. 
See the Price Adjustments after Order Has Processed help article for more information on this process.
Directly Removing Learners via the Accounts Screen
You can remove a Learner from a Course, Track, or Path via the Admin Accounts screen. This will not affect their Product purchase, if any. Login to the Administrative side of your database, go to Accounts, and use the Search tools to find the Learner's Account. Click on the LMS button.
Click on the Remove Icon from the Courses, Tracks, or Paths tab. You will see a confirmation popup. Click the "OK" button to remove.
Note: If the Learner is enrolled in a Track, then you cannot remove a Course that is part of that Track. You must remove the entire Track. Likewise for Paths -- you cannot remove a Course or Track that is part of the Path, you must remove the entire Path.
Directly Removing Learners via the Course's Manage Accounts Modal
Login to the Administrative side of your database, go to Accounts, and use the Search tools to find the Learner's Account. Click on the LMS button. Unlike with directly enrolling via the Admin Accounts screen, your Admin Account first needs Review User permissions for the Course. Also unlike the Admin Accounts enrollment, you can only enroll Learners into Courses -- you cannot enroll Learners into Tracks or Paths via this method.
Assigning a Course Review User or Group
Administrators who have been assigned to a Course as the Course Review User can add and remove Learners from Courses directly from the Admin. Groups of Users, or individual Users, can be assigned to a Course as Reviewers.
To assign an individual User, log into the Administrative Console and navigate to Courses. Click to Edit a Course.
You will see the Edit Course screen. In the Assignment section, choose "Course Review Users", drag the User who will manage this Course's Learners to the Assigned column, and ensure that they are set to "Apply".
Alternately, if there is a User Group whose members should be Course Review Users, choose "Course Review User Groups", drag the User Group whose members will manage this Course's Learners to the Assigned column, and ensure that they are set to "Apply".
Enrolling Learners from the Course List Page
Navigate to the Course list page, and click on the Manage Accounts button.
You will see a list of all Learners enrolled in the Course. Click the Garbage Can Icon to remove them.
Add Learners to the Course by using the searchbox.
Once you select one you can click the green plus button to add the course to their account. If you check the Notify User box it will send the account the “Course Added By Upload” email message in the database to the account holder.
The filter Term Start Range and End Range will let you sort by term date (if a course goes for years and years they can search for only the ones enrolled currently – note that Term Date is either the date enrolled or the course start date).