To edit the reason of complaint, you have to: 

1. Go to the Complaints Reasons tab of the Configurations tab
2. Hover the cursor on reason for the complaint you want to edit
3. Click "Edit" button
4. In the right panel, change the description of the complaint
5. Accept the changes by clicking the orange "Edit" button in the left panel

To remove the reason for the complaint:

1. Go to the Complaints Reasons tab of the Configurations tab
2. Hover the cursor on reason for the complaint you want to remove
3. Click "Remove" button