To unassign a custom subcategory:
1. Click on Settings in the menu bar.
2. Under the Basic Settings page click on Categories.
3. Click on the main category under which your custom subcategory is located.
4. Touch and hold the custom subcategory you want unassigned.
5. A confirmation window will appear; click on the custom subcategory again.
6. Another screen will appear asking you to confirm. Click Yes.
Please note that once the custom subcategory is unassigned it cannot be used again until you assign it to another category.