4GB iPod 2008 unable export/import to iMac2014

Any tips would be greatly appreciated for this problem:

2008 I purchased a 4GB iPod, and purchased and downloaded 80 songs.

Since then I've been unable to sync this iPod to more songs purchased. I cannot import the 2008 original songs to the desktop iMac, nor can I export my updated iTunes song library to the 4GB iPod. The iPod has the most recent version of iTunes. iTunes also recognizes the device (4GB iPod), but the iMac doesn't appear to have a feature to "add" another device (the 4GB iPod). I have only 4 recognized/authorized devices.

Thank you!

DrJOT