some background knowledge you should know

windows automatic update can be controlled by,

1)group policy
2)an administrative account

group policy overwrites local admin. the two suggestions i provided earlier, the first one is for local admin, the second one is from group policy. the local admin's access to automatic update can also be disabled from group policy. in your case, sounds like your account doesn't have access to windows automatic update. thats why the window is grayed out.