Don't use C2 image editor. It's only meant for place holder art or temporary changes.
I echo this statement. You can make more detailed final assets with image editing programs and there are free programs, such as GIMP, to do this. Additionally, it's better for performance to create sprites of the size you want in an image editing program and then import them through the Sprite Editor, so they snap to that size and don't require resizing. Resizing the sprite object still has the same specifications as the larger version.