I'm more comfortable with resizing/cropping images in Paint.NET. My wife needs to submit a portrait for something and the requirements are a 3x5 300 DPI JPG or TIFF in CMYK. I can handle the size and resolution, but I have no clue how to save an image as CMYK. I'm clueless enough that I don't even know if "save image as CMYK" is the wrong thing to ask.
I found a Paint .NET plugin that seems like it does separation, but it doesn't mention if it saves the image so it is a CMYK image. I found an article about similar GIMP plugins but I'm still not sure if it's right.
I've got a 300 DPI bitmap appropriately sized and I'm assuming it's in RGB since I haven't fiddled with anything. Is there a free, easy process by which I can turn this into a JPG/TIFF with the CMYK color space?