Be very careful with this step because this will help you avoid electric shock.
Rock the outer panel of the service panel backward (as shown) or pull straight out. You want to be absolutely certain that you do not accidentally touch components inside the service panel with the edge of the outer panel--or with anything else--as electric shock will result.
You are now dealing with high voltage. If you touch the wrong components inside, a fatal electric shock is possible. This is not the same as a shock received from an outlet in your house. This is power coming straight into your house from the exterior service drop. Please read further here about the highly dangerous service wire lugs.