I am not sure what you are asking for here. Where do you want to install the package you are looking for - your DNS-320, router or computer?
If you can see the router mounted USB hard disk in Networks in windows explorer (assuming you are using windows) then it should just be a D&D operation to transfer the files. It is a little different with other operating systems but the principle is the same.
On the other hand, if you want to use the router mounted hard disk for backup then just use the external backup that the NAS provides.