Transferring music from iPhone to pc?

I have a iPhone 3GS but I bought a new iPhone 4 and I want all my music from the iPhone 3GS to my pc and then put it onto to the iPhone 4. I have iTunes please help in details thank you.

All you need to do it take the cord plug one end into your phone the other into the computer like your charging it and go onto itunes press iphone and then press sync and at the top it will tell you when it is done

Use this method http://igeekshome.com/2013/07/01/best-way-to-copy-songs-from-iphone-and-ipod-to-computer/