Change the string

        'You have pushed the button this many times'

        to

        'You have clicked the button this many times'

        
           Important:
  Do not stop your app. Let your app run.

Save your changes: invoke Save All, or click Hot Reload
  
.

You’ll see the updated string in the running app almost immediately.

Profile or release runs

Important:
  Do not test the performance of your app with debug and
  hot reload enabled.

So far you’ve been running your app in debug mode. Debug
mode trades performance for useful developer features such
as hot reload and step debugging. It’s not unexpected to
see slow performance and janky animations in debug mode.
Once you are ready to analyze performance or release your
app, you’ll want to use Flutter’s “profile” or “release”
build modes. For more details, see Flutter’s build modes.