syncing apps with new computer iPhone

Seems like I am missing something simple here-- I bought a new computer and installed a new iTunes on it. I successfully synced the music but for some reason I cant sync the apps. When I look at the App screen on iTunes, the Sync Apps button is not clicked, but when I click it, it says Are you sure you want to sync apps? All existing apps and their data on your iPhone will be replaced with apps from this iTunes library. But I added some data to my iPhone apps since I first synced the phone to the new iTunes.
Dell PC Windows 7