I still think it's a good idea for you to learn how to do this yourself. I'll post a tutorial if you like.
An easier way to do it, is you just invert the colours, Image>Invert colours, in MS Paint. This will change the lines to cyan and magenta but they can be converted to black by going to image attributes and selecting black and white which will also reduce the disk space requirements considerably. Note that MS Paint is poor at converting to monochrome, anything that's not white will be converted to black and there's no dithering.