can not manual control time zone macbook air
I have a Macbook Air with El Capitan 10.11.4 - I am UNABLE to manually control the time zones. The time zone setting has "automatically detect time zones" checked and it won't let me uncheck it. Anyone know how I can uncheck this? I operate in multiple time zones and having my Mac change it on me is very confusing (just today a meeting was move 5 hours - the exact time difference between UK and NYC and here I am at the meeting 5 hours early).
thanks for any advice!
MacBook Air (13-inch Mid 2013), OS X El Capitan (10.11.4)