Kola, to make manual watermarking work you need to set Apply watermark during any upload (not for selected post types).
Watermark will not be removed if you apply it again – it will be applied again. If you’d like to remove it you need to regenerate images using Ajax Thumbnails Rebuild or Regenerate Thumbnails plugin.
How to Get Support
After you register and login to the site, you may post all plugin support questions in the Support Forum.
If you need to provide private info, please create a ticket and then reply to it using Set as private reply option.