You can remove students from your student list directly on your "Students" dashboard. Find the student you want to remove and click (or tap) the 3 small dots at the top right of the student card. That will reveal several options, including the "remove" option:

You can also remove a student by visiting their student detail page and editing the student. Click the small pencil icon to bring up the "edit student" interface, where you will see the "Remove" button: