There are also enhancements to the performance of the startup sequence - most notably providing a more reliable boot sequence following a full depletion of the battery – as well as enhancements to camera performance when utilizing the popular “pocket-to-photo” feature that allows users to open the camera application on a locked device with a simple press of the dedicated shutter button."-Nokia
Once your Nokia Lumia 900 shows the notification that the update has been received, you need to hook it up to your computer to complete the process. Windows users will use Zune for Windows while Mac users will need Windows Phone 7 Connector. There are three separate updates involved and Nokia says it should take you about 30 minutes to complete.