iTunes 10.6.3 update for Windows and Mac is available now, which includes support for just released iOS 6 beta for developers and strongly recommended to test iOS 6 beta.
You can download iTunes 10.6.3 via Software Update or using direct links below.
Download iTunes 10.6.3 for Mac
Download iTunes 10.6.3 for Windows
See also:
iOS 6 Beta for Developers
iOS 6 New Features