Stop Opera from auto updating

Since yesterday, I'm having a problem with auto update from Opera. Until yesterday I had no problem. I'm in OS X Mountain Lion 10.8.5, and the last supported version is Opera 37.0.2178.54. Now it automatically updates to 48.0.2685.39 and after I close Opera I cannot open Opera again because it tells me “This version is not supported, you need 10.9”. In version 37, there is no preference setting to turn off autoupdate - you get it whether you want it or not. How can I stop Opera from auto updating? I want to be in version 37, which is supported in my operating system.