Licence key ownership change

I have bought a licence key from an ex user, we are both unable to delete his details from the system in order to activate it for myself.

I have his old email and password as well as the licence key but I am still unable to erase his details, if I was to pass these details on to you (support) could you change the details or at least erase his from the licence key in order that I can register the licence to my computer?