In the left hand (local) main pane, navigate (just like you would in Explorer) to your Ning Archive folder where you can see all the '.json' files and folders (members, discussions, music, videos etc.).
In the right hand pane navigate to the folder where your Jamroom is installed. This will typically be /sites/yourdomaincom.jamroomhosting.com/public_html
When there, create a folder called 'Ning_Archive'. The easiest way to do this is to right click in the white space of the right hand pane and select 'create directory', then enter the directory/folder name. When done, navigate to that folder.
Now we are ready to upload the Ning archive.
Select all of the archive files and folders in the local (left hand) pane (use Ctrl-A for quicknesss) then drag and drop them into the empty server (right hand) pane. That's it. Sit back and watch it happen. If you have a large archive this process could take a while, but you can check its progress at any time by looking at the info along the bottom of the Filezilla pane.