This issue is tricky, and you're really better off starting with a clean slate if at all possible. Last I heard, there was no good way to uninstall the e-commerce modules, removing necessary rows from the database and clearing Drupal's caches. The following thread has some sort of a checklist you can use to make this work, but it has some manual tinkering and is not an ideal situation:

http://www.ubercart.org/forum/support/213/moving_e_commerce_module_uberc...