There are several methods of deleting songs from the iPod and/or iTunes, and the method you choose depends on the settings you have selected for your iPod.
If you have the iPod set to automatically transfer songs, and you no longer want a copy of those songs on either the iPod or in iTunes, simply delete the songs in iTunes. Highlight the songs you no longer want then right click and select "clear", or from the edit menu select "clear". Next time you connect the iPod, the songs will be deleted from there also.
Only do this if you no longer want the songs on both the iPod and your computer.
You can also use the "only update checked songs" method in the iPod options (right click on the iPod in the source list in iTunes and select options, then select "only update checked songs"). With this preference checked, you can remove the check mark from the songs in iTunes that you no longer want on the iPod. The next time you connect the iPod, those unchecked songs will be removed from the iPod whilst still being retained in iTunes. You can check and uncheck songs as you change your mind about what songs you want to put on the iPod. Songs that have no check mark against them will be skipped over when played back in iTunes.
If you have the iPod set to manually manage your songs, and you want to delete the song from the iPod
only, then select the iPod in the source list of iTunes, or click on the "music" option underneath it to show all your songs. Highlight the song(s) you no longer want on the iPod, right click and select "clear", or use the edit menu as previously mentioned.
This method only deletes the songs from the iPod, so if you no longer want the song in iTunes also, you'll need to delete it from there separately using the method above.
If you are using iTunes version 7 or later, all these settings can be found in the summary screen.
If you want to delete everything from the iPod and completely erase the hard drive and start from scratch, then you can
restore the iPod to factory settings.
Only do this if you have the songs in your iTunes library, or a back up somewhere other than the iPod itself.
See also:
Deleting songs and playlists from your iPod.