In manual mode, on ipod side, first delete from play list, then delete from library, the song will permanently be removed, check info from ABOUT, u will find u have less songs and more free space, remember: delete from play list won't delete the lete them from your library then update your 'pod - unwanted tunes are history!
When you attach your iPod to your computer and it syncs with iTunes, turn off the auto-sync. Don't select any music to be added, and manually sync it. Voila--deleted!
There are two options,you can connect the ipod to system using the datacable and select all the songs and delete or just right click and click on Format,immediately it will show a message that,"this will delete all details" then click ok.
Go into your Itunes library and delete all of the songs your "your ipod" after this just update it and it will clear all of the songs that have previously been on it.
First you want to download ITunes. After you do this plug your ipod into your usb drive until it pops up on itunes. Click on the ipod under the itunes menu and you will see something that says format ipod. Click on that and it will erase the songs on your ipod for you.