In this tutorial we will teach you how to get Windows Phone 7.8 update for your WP7.5 device. Forcing the WP7.8 update requires patience and the ability to disconnect your computer from the internet.
First turn wifi and data connection off on your windows phone and computer. Then connect to Zune on the computer. Then go to settings and check for an update and as soon as you click the “Update” link in the settings you’ll need to disconnect from the internet.
Zune will tell you it cannot check updates right now. Simply turn Wifi / Internet on your computer and it will tell you that update is available.
Again timing is the key here. Here are the steps one more time.
Turn off WiFi and data on your phone
Connect to Zune
In Zune, go to Settings and check for an update
As soon as you click “Update” disconnect from the internet.
After Zune says it can’t check for an update reconnect to the internet
There should be an update ready this time
Follow along with the wizard to complete the update