Help resetting iOS 6 iPhone

You can't reset your phone to new while retaining the contacts and photos. You have to reset it and restore those.

 

Depends on if your contacts and calendars are in the cloud (iCloud/gmail/outlook). If they are, you could completely wipe the device and then simply re-add the cloud based accounts. But you'd need to copy the photos from the device and then sync them back to it

You can wipe your phone through settings -> general -> reset -> erase all content and settings (backup your phone first though).

Once this is complete you can set the device up as a new phone and then pull all your calendar and contact information from the cloud.