One at a time is the only way I know of within the NS Console. I can think of a few ways to try to do this in bulk, but you would want to test this in a lab first. I haven't tried any of them myself, but if I was going to have to change this for a few hundred packages, I'd probably try number 3 first (again, in a test environment first).
1) You could script something that exports the package XML, updates the location of the source files, then re-imports it using importexportutil.exe found in the bin folder.
2) Use the SDK to do the same steps in number 1, but use the methods available in the SDK to update the source
3) See if a simple update to the [Package Location] field of the SWDPackage table would work.