I would like to modify my order

Hello,
I ordered on 13/02/2016 the following article.
State of the last command HobbyKing.com ®
Number of order:20013242847
$Valeur:98.23
Statut:Payé, current(in class) Treatment(Processing)...

I would like to modify my order the by replacing the article ordered by the following article:
HMF U580 Pro Carbon Fiber Folding Quadcopter Kit, Produit ID: 571000021-0

I shall settle(adjust) the complement.
How is it necessary to make?
Thank you for your answer.
Dionisio GARCIA
Email: denis.garcia83@orange.fr