The update takes about 5 to 10 minutes to install once it is downloaded, and you won't be able to make or take calls during this time. We'd suggest using a Wi-Fi connection while downloading the update so that you don't use your precious data allowance. And of course, you should have your battery charged to at least 50% before starting the process.
If you've updated your Nokia Lumia 1520, let us know if you can see any changes to your phablet. You can leave your comments in the box below.
source: @Nawzil8 via WMPoweruser