Watch this video and learn one method to change a tire on a road or triathlon bike
There are many different ways to change a flat. There really is not one perfect method. This video shows one way to change a tire using tire levers. I suggest that you learn all of the methods and find the one that works best for you.
I must confess that I rarely use the method demonstrated in this video. I find it too constricting. I much prefer the non-tool method that I teach in my Basic Bicycle Maintenance course. Watch this video and the others on maintaining your bike.