how to import music on ipod nano to new itunes library on new computer?

I haven't used my ipod in years... Truly it's been about 5 yrs. In those 5 yrs, I've bought a couple new computers... I recently wanted
add/delete music on the ipod but I can't? When I open the iTunes, it shows all of the music I have on the ipod but I can't play or delete anything. I tried researching how to import music but my ipod doesn't show up as a removable disk on my hp laptop. Help?