The easiest way is of course not to install the updater when you install flash (I never install updaters if they are optional an I turn them off if they are not). But, for most it’s probably too late for that, unless you’re rolling back to a previous version. If you are rolling back, don’t install the auto updater.
Right here Adobe tells you how to disable the auto updates for flash. Yes, I have done this on my computer. It works fine.