Hi Andres,
Could you clarify your question? Are you trying to split a single image into four equal parts? Or are you trying to enlarge an image?
If you want to split the image, you can use the selection tools while holding shift on your keyboard to select perfect squares. From there, you can crop the image to your selection, four separate times, to get your four separate frames of the image.
If you're trying to enlarge your image, you can resize it from within Paint.NET but I don't recommend that option because it will leave it blurry and pixelated
Hope that helps,
Nab