Construct 2 games updates automaticly in the background but the update will not show until you have reloaded the game in the browser.
You could use the "Browser" On Update Ready...
And use that to show a reload-button, that reloads the browser when clicked.
Kind of like this:
This is the simplest way I can think of to do it.
The downside is that - the player may have started the game and played for a while when the refresh-button gets visible. And if the player clicks it, all game progress will be lost.