If you have not started it you can stop the process. If you are already in one then you will have to let it fail by missing three payments. Your credit record will be stuffed for the full six years. Can I ask why you want to cancel it?
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
As Kallis says, if you are already in the IVA, you can allow it to failby missing three payments. However, your creditors will then be able to resume collection / enforcement of the loans, if they so wish, having added back lost interest and charges and there is no guarantee that they will co-operate with any other solution you might propose.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk