First of all, if you’re device is not Jailbroken, you’re out of luck. Well, try iFunBox maybe it will work, I can’t test it, but if it works for you I’d appreciate a comment. Jailbreaking is not difficult, but you’d have to learn a few things. Check out this site for more info – http://www.iphonehacks.com/jailbreak-apps
Jaibreaking adds a lot of features not available or blocked in a factory build device. I’m not going to go in all the details, if you’re curious, google is your friend, at least for now 🙂
So, for those how have a jailbroken device, there is no problem deleting 300MB of Wallpapers. Personally I don’t like most of them and with only 16GB of storage I’m always running out of memory – deleting all these wallpapers is a breeze.
Download iFile from Cydia package, or an app like iFunBox, navigate to Wallpapers (in iFunBox) or Disk/Library/Wallpaper (/var/stash/Library/Wallpaper/