how t ouploadmy itunes from back up

Go to the external hard drive, copy your content to your documents or whatsoever, then open iTunes, drag all music to iTunes when Music has been selected in the sidebar. Note that you should keep your music in the same documents folder.

If iTunes was "backed up" by copying the ENTIRE iTunes folder to the external drive, simply copy that same folder to the new computer and open iTunes.

No need to import anything or create a new library and lose all the playlists and playcounts.