How to delete duplicate songs downloaded from itunes to my iphone?

When i download and sync my iphone it downloads the music twice. It doesn't happen on my ipod or on my itunes music list on my desktop how do i delete the extra song from my iphone

Added (1). There's no duplicate in my itunes list!

Go to the top toolbar in itunes and click file then under file click display duplicates, delete the songs on the list then sync your iphone

Instructions

1

Connect your iPhone to your computer.
2

Double-click on the iTunes icon on your desktop if the program does not open automatically.
3

Click "File."
4

Click "Show Duplicates." iTunes will display a list of songs in your music library and their duplicates.
5

Right-click on each duplicate and click "Delete."
6

Click on your iPhone on the left-hand side of the screen.
7

Click on the "Summary" tab.
8

Click "Sync" to re-sync your iPhone with your library and remove duplicate songs on the iPhone.

Plug your iphone into your computer - go to its music/playlist - find a duplicate - click on it (turn it blue) - press delete.