First you need to go to System Preferences. You can do so by following the green arrow in the picture below and clicking the "System Preferences" icon:


Step 2

Then, after the application is loaded up, press the "Mouse" button in the System Preferences window.



Step 3

Once you're in the Mouse subsection, check off the square below the arrow pointing down and change the bar that says "Left" to "Right" by pressing it and then selecting Right. And that's it, you're all set! Now you can right click by pressing the right side of the mouse and left click by pressing the left side of the mouse.