Take a look at this post.
In this user's case, the font settings are stored in:
/home/user/.config/pcmanfm/LXDE/pcmanfm.conf
I haven't verified this on Raspbian, but poking around the .config folder might reveal a relevant file of sub-folder.
Open a Terminal (CTRL-ALT-T should work, if you can't find a shortcut), then navigate the folders using the cd command. Terminal should open with you already located at /home/<username>, so just type cd .config and hit enter. ls will list files in the current folder, you may need to use cd a few more times. In the example above, you would have to cd pcmanfm then cd LXDE, and then ls should show you the files, look for a relevant one (pcmanfm.conf in the example above).
Once you've found a file you want to look at or edit, you have a few options. The world is divided into two factions: those who like nano, and those who like vi. Type nano <filename> and hit enter, if it says it's not installed, type vi <filename> hit enter and hold your breath.
Nano is the easier one to use, but if you must use vi, scroll up and down using the arrow keys, when you want to type something, hit i first (to switch to "insert mode"), then type. Try not to use backspace, delete or the arrow keys while in insert mode, some keyboards will screw up your text file. If you must, hit ESC to return to "non-insert mode," and hit i again when you are ready to type. When you are done, hit ESC, then type (it will appear at the very bottom of the screen) :x (this will save and close). If you bugger something up and want to quit without saving, hit ESC and type :q!.
