How to back up your IPhone data to another phone using ITunes?

I have an IPhone 4 and i'm trying to back my data onto a IPhone 4s but i don't know how (It is not a new phone) Can anyone help me?

Just set the new phone up as a new phone and you will get the option to if you want to restore a back up from the old phone.

One way is to use iTunes, I think Apple should offer an option to do that.
The other way is to use iphone transfer software. They can help users to transfer iPhone data directly from the other iPhone easily. But most of them can't deal with App, they can't transfer App from one iPhone to another. But I think you can redownload them to the new iPhone using your iTunes account and it's really easy to do that. Aiseesoft provides this kind of software and they are on the top list of this market. You can download the trial version of it and have a try first.