Changing personal name on software for editing?

Hello,

I am having problems with changing the license name of the software. I am using my sons old computer - when editing proofs his name is appearing even though I have changed it to mine in the preferences.

I have also changed the PC name through the control panel with no luck.

I am using the trial version currently, but planning to purchase after its up - Any help with this would be great.

Edit: Under identity in preferences the login name is greyed out with sons name which I can't edit...

Many thanks,

Peter