In order to delete an App Category, you should have to go through the following steps;
Step 1: From the admin left panel, click on Settings.
Step 2: From the options that open, select App & URLs.
Step 3: From App & URLs window select ‘Categories’.
Step 4: The interface that opens will show a list of apps separated by categories.
Step 5: Find the app category you wish to change the name of and click Edit.
Step 6: This will open up a pop up. Click on the Delete button.
Your app category will be successfully deleted.