As you know some of us have had no luck getting the official update. So here is a guide to update.
http://www.windowsphonehacker.com/articles/want_windows_phone_7.8_now_try_this_easy_tool-01-31-13
It does three separate updates. Takes about half hour to do all, just leave it be until it says “All Done”.
Read the instructions. They are easy, but their is a disclaimer as with anything like this. Basically you need to download the program and then the Microsoft updater (it does this for you). Extract the updater, and install the 32/64 bit version depending on your windows, and run the original program.
I was shocked by how much extra screen real estate the update gives. I have to admit I didnt like the look at first, but once you resize some tiles and make it your own, it is a vast improvement. It worked for me using a bought unlocked Nokia Lumia 800 on T-Mobile.
