Hi Super Moon,
I see that you're looking to remove some songs on your iPod to make room for new content to sync over. I'd like to help you remove these songs from your device.
To easily manage your content, I'd recommend using the "Manually manage music and videos" setting.
Please follow the instructions here to make sure this setting is enabled:
Check to make sure that the "Manually manage music and videos" option is turned on:
- Connect your device to your computer.
- Open iTunes. Make sure that you have the latest version.
- Locate and click on your device.
- In the left sidebar, click Summary.
- Scroll down to the Options section.
- Click the box next to "Manually manage music and videos."
- Click Apply.
Once you've done this, select your iPod from the iTunes sidebar.
If you need to enable the sidebar in iTunes, you can do this using View > Show Sidebar. Click the disclosure triangle next to the iPod, then choose "Music" from the indented list under the iPod.
This will show you all of the songs that you're currently storing on your iPod.
Deleting the HKEY Registry keys of Windows one by one
From here, you can select the songs that you no longer want on the device, then press the delete key on your keyboard to remove them.
The steps quoted above were taken from this Apple resource:
Move content from iTunes on your computer to your iPhone, iPad, or iPod touch - Apple Support