Deleting a distribution wipes out all the data associated with that distribution. Thus, use good judgment when you want to go for deleting a distribution.
UpRaise users with sufficient permissions can delete distribution from distributions tab under Forms menu item of administration section. Clicking on the drop-down arrow on 'distribute or view responses' button opens up the delete option. 'Distribute and view responses' buttons will be available depending on the status of distribution.
Clicking on delete asks for a confirmation, which once confirmed will remove the distribution & associated responses.