Once the power has been turned off to the electrical panel by either turning off the MAIN breaker or the breaker serving the panel you working on (if it is a remote sub-panel), the next step is to remove the front door and cover plate.
Remove the screws holding the door into position and carefully remove the door assembly.
Once the door and plate are removed you need to remove two knockout tabs for the double height 240 volt breaker. The way you remove the tabs may vary from this tutorial due to manufacturer's design, but it will be a knockout that you either loosen with a screwdriver blade and then remove with pliers (not shown) or the type shown here where you grab the tab with pliers to remove.
