Hi Don,
It all depends on the file format you start from. If you have a STL, you would basically have to cut and remodel bits as it is not really a format intended for modifications. Just my opinion, but you'd probably be better off redesigning from scratch.

If you have a native format of something else, it might be possible. For instance, you can "rig" a model in Zbrush, allowing you to modify the pose. We're talking proprietary software and skilled design here. I'm pretty sure that is not the file you purchased.

Good luck