It could be complicated. He'd still need your password to reset the password. Is your user profile a local profile or an email address (in my case it's a hotmail email address, but some laptops are set up to use a local username and password)? If it's an email address you can log in to it on any other computer and change the password then tell him the new one and see if that works. If it's a local one then it's not as easy as that and a factory reset might be the only way. You would have to do that, though, as he's only a guest user. The administrator has to do anything like that.