There's this thing called Google ...
The instructions on what to do are in the download as well as a list of what is updated or fixed - and that is also shown on the download page.
for upgrade your camera firmware you must perform this step:
1) go to canon site
2) find the last firmware for canon 5D Mark II and download the zip file into your computer for windows or mac
3) after you have download the file extract it into a folder
4) copy the file 5D200212.FIR in an empty CF card
5) insert the CF card into your camera
6) reply to the question on your camera dispay for to start the upgrade
7) wait after the upgrade is complete
VERY IMPORTANT: perfom the upgrade with full charge of battery
The actual version is 2.1.2
tell me about your upgrade process