thanks for that link, when I run VMwareUpdateManagerUtility.exe on the vum server it initially asks for a username to open it, if I use ad\vum user it says the vcenter username and password you entered are incorrect so there is my issue as suspected by daphnissov. So using your link to get round it I use administrator@vsphere.local which then lets me get to the settings which is pictured on the link you sent. But when I change the user in the re-register section to administrator@vsphere.local it says it's completed but it reverts back to my ad\vum user.
FYI the ad\vum user is in the administrators group in the roles section.