dcb -
If the project exists in Paratext it is generally a better idea to delete it from Paratext. There you can choose where it should be removed from (your computer, the registry, the S/R serve, or any combination). If the project is still registered and availble through S/R, I would recommend downloading the project and then deleting it from within Paratext with the option to delete in all locations.
All of this depends upon your role in the project. I would also recommend reviewing who else is a member of the project (if anyone) so that you can notify them that the proejct is being deleted.
It is a bit more complicated in the registry. You should delete the project from the server before you delete the registration. Under the registration tab for the project there are options to delete and unlink. The delete option will remove the project from the S/R server. Unlink will delete the guid, but leave the project in the registry. Both options show warnings about what will be done.
You can delete the registration from the projects list:
