I'm not really familiar with ucblogo, but I looked it up (ref: Berkeley Logo (UCBLogo)
It looks like the files don't actually contain image data, but instructions for the ucblogo program to create the image.
I doubt that you'll find an easy way to convert the logo files (*.lg?) to standard image formats, but I think you should be able to do it with a screen capture program. I like to use The Gimp for this kind of thing, but you could probably find a lot of different graphics tools that do this.
You could use the import
command from the previously mentioned ImageMagick
suite. You might even be able to do it in a sequence with the UCBLogo program from a shell script depending on how it's command-line options work.