cctible according to the T and Cs if you cancel your flights and request a refund them "Qmiles and Cash collected is forfeited Only airport and government taxes will be refunded." In other words your Qmiles/Qcredits will be lost.
However you may change your flights at the fees listed on http://www.qatarairways.com/Privileg...ge?mid=5&sid=1.

I seem to remember that someone reported that they had cancelled the flights but not the upgrade ticket and were able to use it at a later date.
I am no expert in this area and I am trying to remember a post from early 2015 so please do not regard my answer as definite. Let more knowledgeable FT members tell you, and me, what the facts are.