The Windows Phone 8 Update 2 emulator is revised to reflect Windows Phone 8 build 8.0.10322. The only change in this update is included support for Visual Studio 2013 RTM. So if you have only this IDE installed on your machine, you will be good to go.
The WP8 Update 3 emulator corresponds to WP8 build 8.0.10492. It brings a new 1080p mode which lets developers preview how their apps would look on such displays. Perhaps this will lead to more apps designed for high-resolution screens, which will appease owners of the Lumia 1520 and future 1080p Windows Phone 8 devices.
If you want to get to grips with the new emulator images, proceed to the links below.
Download: Windows Phone SDK 8.0 Update for Windows Phone 8.0.10322
Download: Windows Phone SDK 8.0 Update 3 Emulators
source: Windows Phone Developer Blog via WMPower user