How to delete music off of my iPhone 4?

How can I delete music off of my iPhone 4?

If you just want to delete one music, slide it in the playing list, and it will show you the delete button.
And if you want to delete in batch, you should login your iTunes from PC or from the iCloud in your iPhone.
For the iPhone 4, after you delete the music, you should sync your iTunes with your iPhone4.

You can uncheck the songs on your iTunes library first, and then sync your iPhone with iTunes, the songs will be deleted off your iPhone. Or you can use a 3rd party software like this iPhone file manager, it can help you delete files easily.