Dear Ms. Sawitree,
As soon as your order has been placed via parts Online you can not cancel it yourselves.
In case you like to cancel something you have to ask me if I can cancel it for you and then it depends which order type you have ordered.
If it is a YSO order there is no chance to cancel something. For YTA orders it is only possible if they are back ordered and not available as they also will be in the system soon.
I hope this helps.