Syncing iPod with iPhone's iTunes

I have a first generation iPod which has all of my old music and apps on it. I also have an iPhone 5 which is synced to my current iTunes library. Basically, I want to sync my old ipod to my current itunes so that everything on the old ipod gets wiped off and all of my current music, apps etc, is synced to the old ipod. So then I would have my iPhone and my iPod with exactly the same music and apps on it.

I thought that when I plugged the old ipod into my PC and synced it with itunes, a message would appear asking if I wanted to sync the itunes library with the ipod, but this didnt happen - my ipod was synced separately. I clicked sync at the bottom of the summary page hoping that it would mean all of my itunes would be synced to the ipod, over riding everything already on it, but this didn't happen either.

There is another option which I am unsure about. That is to click 'sync entire music library' which is a button at the top of the music tab when the ipod is plugged in. Does this mean that all of my current itunes (which is on the PC the ipod is plugged into) will be synced to the old ipod, or does it mean that all of the content on the old ipod will be synced to the PC and delete all of my current itunes? Is this how to sync my old ipod to my current itunes or is there another way?

Sorry if this sounds confusing but I am a little unsure due to the fact that my ipod already has content on it, so I don't want to sync it and end up deleting all of my current itunes content.

Thank you 🙂