Find the student you want to remove by clicking on 'English Every Day' in the menu on the left, then on 'Classes'. Then select the student's current class.
Click on the name of the student. It'll take you to their page with the English Every Day statistics and the class they're in.
Right under the student's name you'll see the options of removing the student from the class, of changing their class or changing their password.
If you click on "Remove from class", the student will no longer appear in the class. You'll still find them in the menu "Students" under "English Every Day". If the student has already created an account last year, you can just change the year in the top right corner to find them.