what should i do with my old ipod nano gen 2

It's a pity that you haven't mentioned what you have done since it's unlikely that you have tried everything. Not only that, but if you had cared to mention what happens when you did try something, then we could go from there.

For now then, we'll have to do it from the beginning:

• If the iPod has previously been synced with another iTunes Library, you will be asked at some point if you wish to erase everything from the iPod and then add content from your current Library. Since you wish to change the music on the iPod, your answer will be yes (but it really will delete all the music currently on the iPod).
• Connect the iPod nano to a computer running iTunes.
• Does it appear in iTunes? If so, click on the icon indicated in my screenshot below:

Now follow the steps in the screenshot below:

• Click on Music (1.)
• Click on the box labelled Sync Music (2.)
• In step (3.), choose either:
  • Entire music library (which will try to add all the music in your library)
  • Selected playlists, artists, albums and genres (in which case, the additional boxes at (4.) will appear)
• If you chose to sync selected playlists, artists, albums and genres, then you can now choose the items you want from the boxes in section (4.)
• Click on the Sync button in the lower right corner of the iTunes window (not shown in screenshots)
• Once the Sync has completed, safely remove the iPod by ejecting it. That's done by clicking on the eject icon at towards the top of the iTunes window (it will be above the battery icon, replacing the double headed arrows shown in the screenshot above).