first of all you need to decode it... you can use Ioncube decoder... from here:
http://bvlist.com/other-downloads/45...er-v1-7-a.html
After that you need to recode it... because that software will not fully decode it.... so you need a coder for that (to recode it)
After that you need to remove all backdoors... (this is how you can null it)
Its a bit hard... right?