To edit or delete  existing Custom Rules, please proceed as follows:

1. Options > Categories & Rules > select the Main Category or Subcategory > Edit (Context Menu) 
2. In 'Custom Rules' you see the existing rules
3. Delete a rule: Context Menu > 'Delete'
4. Edit a rule: Context Menu > 'Edit'
5. You can also add another new rule here for the category (+-Button in the lower left)
6. Click on 'Done'  and then on 'Save' to save the changes

To edit or delete  existing System Rules, please proceed as follows:

1. Options > Categories & Rules > select the Main Category or Subcategory > Edit (Context Menu)
2. In 'System Rules' you see the existing rules
3. Click on the +-Button in the lower left corner
4. Now you see the list of system rules. Select the one(s) you want to add to the category you selected in the beginning. 
5. Click on 'Done'  and then on 'Save' to save the changes