The Large One
Who's Next?
yes it does have layers
Right, I'm writing along the lines of assuming Paint works in the same way as Photoshop.
You need to create a new layer, and place it under the image you wish to edit. Then make sure you select the layer that the image is on, and rub out the bits of the image you don't want.
Alternatively, you can use a clipping path, but again I don't know if Paint has that.
If the whole of the artwork is being created in Paint, I'd go for the former rather than the latter.