As long as the class set up in Admin>classes has not been used you will be able to delete this from your end. (If the class has been used and you are certain you need it removing, you can request for us to remove this for you).
The first thing you need to do is go to Admin>Classes and find the class you want to remove.
Click the black cog icon to expand and show the staff and students assigned.
Next click the red crosses to remove the staff and students from this class. For students there is a Remove All button at the bottom.
Once all the staff and students are removed the class will now show in red to indicate it is empty. You can now just click on the red cross to remove this class.