How to get music off of a laptop onto my Iphone 4?

I had recently gotten a new laptop and new music on itunes, and it's not letting me drag and drop any music onto my phone. I've tried looking for solutions but the only one I've found is to manage music manually, but there's a pop up box that say's that if I continue it'll erase everything off my phone. Is there a way to drag and drop music without syncing or deleting any of the things on my phone now?

You may remove the DRM protection off your songs. NoteBurner M4P Audio Converter is a useful DRM audio remove tool which make you easy to transfer the audio files from iTunes to other media players without syncing.