There is no way to change the resolution of the game, unfortunately. The only way to make the window larger is to run the game in full screen mode - you can do this by setting "windowed = 0" in the gameoptions.ini file in the game folder.
However, if the font is illegible I suspect you have another problem here. I use a 1680x1050 screen myself and the font is easily readable, but on some computers there is a rare bug which causes the text to be incredibly small
like this. If that looks similar to what you're seeing, try changing the font in gameoptions.ini to something other than the default settings - try this for example:
font = Verdana
font_size = 14