How to recover when after updating Ndivia driver, the graphic driver is disabled

I've done the classic sudo apt-get update && sudo apt-get upgrade

I've been asked to update to latest Nvidia drivers. After a lot of "update" lines, I reboot. Now, when I boot I get this: two black screens, only the top "on" with a mouse I can't even move. My keyboard works, but (I guess!) the video driver is so broken that when I try to get a console via Ctrl + Alt + F1-F6, nothing happens. If I press 7 times Ctrl + Alt + Del it works and reboot. Here are my two screens, blank and of no use:

When I boot, I try to edit the boot option by typing e and I didn't find on the Web the option to add / remove to boot as command line and force installation of the old driver.

• Should I comment "load_video"? If so, how to comment?
• Should I comment "gfx_mode $linux_gfx_mode"? If so, how to comment?
• Should I add / remove an option after "linux /boot/vmlinuz-...blabla quiet splash"?