After you've created a new class, you can see a preview card in your Classes. You can edit any existing class by clicking on the name of the class, as found on its preview card. This action will lead you to a dashboard. Clicking on the pencil icon, will enable you to edit any of the properties available, through a popup window. You will also be able to create or view your Subjects for this Class.
You can delete any existing class by clicking on the name of the class, as found on its preview card. This action will lead you to a dashboard. Clicking on Overflow menu (signified by three dots [⋮]) on the top right hand side of the screen, will give you an option to delete the class.