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

1. Settings > Categories & Rules > select the Main Category or Subcategory > Edit (upper right corner) 
2. 'Edit Custom Rules'
3. Delete a rule: Tap on 'Remove' 
4. Edit a rule: Tap on the line you want to edit
5. You can also add another new rule here for the category
6. Tap on 'Done'  and then on 'Save' to save the changes

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

1. Settings > Categories & Rules > select the Main Category or Subcategory
2. Tap on 'Edit System Rules' 
3. Now you see the list of system rules. Select the one(s) you want to add to the category you selected in the beginning. 
4. Tap on 'Done'  and then on 'Save' to save the changes