You only have to remove the two wires at the bottom of the controller. I recommend to send the controller in a padded envelope to save shipping costs.
You can send it back to:
Aqua Computer
Gelliehaeuser Str. 1
37130 Gleichen
GERMANY
Please include a short description of the problem and if possible a copy of the invoice. If the problem is covered by warranty you don't have to pay anything for the repair and shipping costs back to you. Otherwise the costs will be somewhere around 15,00 EUR.