How to delete songs that are only on my iPhone and aren't on my iTunes?

I downloaded songs on my phone that I had already bought because they weren't on my iTunes after I had transferred songs from desktop to laptop. Once the songs weren't transferred to my laptop from the phone, I downloaded them on the laptop and synced it onto my phone. Now I have duplicates of the songs on my phone, and I want to delete the duplicates.

I don't know why people insist on syncing their phones and iPods - I never do and manage to have put hundreds of songs on my iPod w/o getting songs I don't want, w/o erasing unneeded songs and w/o duplicates.

If you can see the dupes on your phone using iTunes when the phone is connected to your computer, just highlight the unwanted songs and hit the delete button.

From now on, don't sync, just use manual management in iTunes. It's worked for me on 1st gen nano, s iPhone 5 and iPad 3.