I don't think you can, but if it is possible it would have to be done
directly through Adobe.
Upgrade Indesign CS6 to CS6 Design standard full edition for Mac need help without costing AN ARM OR A LEG!!
The standalone > suite upgrade path was removed when CS6 arrived.
Owners of a CS5 or CS5.5 suite edition qualify for upgrade pricing to a CS6 suite edition. Owners of an individual CS5 or CS5.5 product qualify for upgrade pricing to the same product but not to a suite edition. Any version earlier than CS5 will not be eligible for upgrade pricing."
Upgrade options now are a) buy the full CS6 suite or b) join the Cloud.
Looks like Bob has it correct. I just went to the Adobe site to buy CS6 Design Standard, and the only options for upgrade are other flavors of the Creative Suite; no stand-alone products are listed. Hope this helps...
Thanks Mikey - i thought this would be the case