It sounds like you already have firmware v2.16, so no need to download and install it again. I suspect you’re a little lost on all of the version numbers (and it can be a little confusing), so I’l give you a quick run down (I apologize in advance if this is old news for you). To start with, the firmware version numbers do not match the hardware version numbers. There’s some correlation, as in some firmwares only work on some hardwares and vice-versa. The other wrench that’s thrown into this is BLDC Tool (the computer application that you use to connect to your VESC to change its parameters). It has some limitations on the firmware versions it supports. The current release of BLDC tool only supports firmware v2.17 and v2.18 to my knowledge.
Now with all that, by “4.12 firmware” do you mean firmware v2.18 (the current release)?
FOC is Field Oriented Control. It’s a different way for the VESC to control the motor. It’s usually a bit quieter than BLDC mode. See here: http://www.electric-skateboard.builders/t/vesc-faq-what-is-foc-field-oriented-control/419
If you haven’t already, I’d recommend reading this: http://www.electric-skateboard.builders/t/new-vesc-user-read-this-complete-walktrough-of-the-vesc/2980