Change OSX encryption filevault password to match login pass

When I first setup my OSX laptop, my filevault and user login password were the same. At bootup, I only had to login once (with my username and password).

I recently changed my OSX password but my filevault / disk encryption password was not changed. Now I have to login twice when I boot up (first with my old pass, then with the new one).

Is there any way to change the disk encryption password so I can be in sync with my login password?

I tried Disk Util > File > Change Password, but it is greyed out.