Removing a softmod can be a dangerous process and is generally not recommended. It would probably be better if you updated the softmod using the softmod any wii guide and then just sold it. I think most buyers will actually think of it as an advantage. However, if you really are hell bent on removing the softmod, I recommend using the guide for removing your softmod. It's somewhere in the recommended faqs guides and tutorials section if I remember correctly.
EDIT: this is the one http://www.wiihacks.com/other-faq-gu...d-any-wii.html