Command Pattern :How does command allows extensible?

I read command pattern here in this link http://ift.tt/1QZv2ET

Its says command pattern " Command pattern is easily extendible, we can add new action methods in receivers and create new Command implementations without changing the client code."

How it is possible client codes has to change if we add new command .Suppose in above code example if I want to add DeleteCommand. Client program main has to change right I mean he was to need code in to client code.

What does the change word means exactly it means ? Does it mean we dont need to change existing code but we can add new code. Is that is the meaning of Extensible of command pattern ??