~ to open the console, then
fov xx
where xx is the desired FOV. 90 usually is enough, but it's to your liking really, so try out different values.
Some people noted that it reverts to default FOV when they load the game and only sticks if they edit the .ini file. It works fine for me though, and I didn't edit anything. If you come across this problem, search the forum, there's a topic with all the ini tweaks.