Double watermark on some images

Hi

I’m using the watermarking for images on my site which works really well but I have a couple of issues that have arisen.

I have resized the watermark since initially installing it however this has now added two watermarks to the image. Is there a way to undo existing watermarks (as the administrator) or to at least override the existing watermark with a new one (or a new size)?

http://wordpress.org/plugins/image-watermark/