Updating your iDevices to iOS6, can be run without iTunes via OTA update, you only need the iDevice itself. Another way to update it is via iTunes. Updating iOS 6 via iTunes is more stable as you download the entire package from Apple server to your Mac or Pc before installation. You can also choose to download without install. The iOS firmware package size for iPhone is about 600MB and 1GB for iPad. You can pause and resume your iOS download within iTunes. Check it out the procedure how to make it.
1. Download 10.7 iTunes version which supports iOS 6.
2. Install it into your Mac/Pc.
3. Turn iTunes 10.7 on and connect your iDevices. Make sure your iDevices have more than 50% battery.
4. Let iTunes recognize your iDevices and complete the normal synchronization.
5. You should see a prompt to indicate the new iOS 6 update available for your iDevices.
6. Select Download Only or Download and Update the iOS. [I selected Download and update and decided to install it afterwards.
7. Wait for download to complete.
8. Installation will be started.
9. Your iDevices will restart after installation.
10. Enjoy your iOS 6 on your iDevices.