iPad-Synced from iTunes library

How did this content get on your iPad, if it wasn't in your iTunes library on your computer?

Connect your iPad to your computer and when it's recognized, click on your iPad to open it in iTunes. You'll see the synced content and you should be able to uncheck it to remove it from the iPad.

This link explains iTunes Sync: Sync your iPhone, iPad, or iPod using iTunes on your computer - Apple Support

A clean restore will certainly help you. You need to delete more things off your device though. I would delete photos you don't need, apps you don't use, text messages, emails, etc. Then do the restore.

You delete content synced from your iTunes library to your iPad the same way you put them there, which is you connect your iPad to your computer and use iTunes to unsycn the content.

Reboot your iPad, then check the storage. Press and hold BOTH the power and home buttons at the SAME time (keep holding past the swipe to shut down) until you see the Apple Logo, then let go. Chances are storage will change.

Sorry, I'm out of suggestions. Either use the Contact Support button at the top, or call Apple at: 1-800-MY-APPLE or schedule an appointment at your Apple Store Genius Bar for assistance.