There are four process you need to do.
1. Create a settings backup
2. Flash an image (It does not matter whether you use image manager or USB flash drive)
3. Restore settings
4. Restore plugins
Using Image Manager to flash is far easier that USB
3 & 4 will not be possible if image is current image older than 4.2
See here
http://www.world-of-satellite.com/sh...-and-Restores/