Sync new iphone off old backup ??

recently purchased new iphone 3gs, and my old 3gs back up is on itunes, i can find it under the devices panel but how can i sync my new iphone off the old back up?
i want to do this to keep all my app data etc.

please help

Thanks in advance

Here's Apple's instructions on that. iTunes: Backing up, updating, and restoring your iPhone, iPad, or iPod touch software

thankyou, i have managed to sort it