You can't -- yet.
The feature was removed in iTunes 11, but it is restored in the latest beta (11.1.6) -- which will likely be released soon (by "soon" I probably mean within the next month or so, but I have no special insight into this).
While there is no issue whatsoever with storing contacts and calendar data in iCloud, some people have legit non-tinfoil-hat reasons for not wanting to store sensitive data remotely. They spoke, Apple listened, and the feature is on its way back.