Open iTunes, navigate to Library and select Music. Right-click on the songs you want to remove and select Delete. After that, connect the iPod and wait it to sync with iTunes and delete the songs. Alternatively, connect the device to your PC, open iTunes and select Manually manage music from the Options menu. Select your iPod from the Devices list and click on a category or a playlist to see all the songs. Right-click on the file you want to remove and select Delete.