Unfortunately, for the moment it is not possible to move a task from one story to another. However, we have already had this request several times and it is logged as a feature request in our TeamPulse. There is also a story in our backlog for this functionality and we are going to implement it in some of our next versions, but it is not scheduled yet.
If you have any other suggestions for features you wish to see in TeamPulse do not hesitate to contact us again.
the Telerik team