How do you update google image/search results?

Question

I have noticed that some websites like Instagram and ask.fm, google does not update their search results.

For example if i have an instagram username like "Qwerty" then i type Qwerty into google (and since google crawls through instagram for usernames) you should get like:

Qwerty (@Qwerty) • Instagram photos and videos.

And when you change your username to "Asdfgh", google should update the results after some days. So that when you type Asdfgh into google you should get this in the search results:

Asdfgh (@Asdfgh) • Instagram photos and videos

But somehow, they don't update. Even after half a year.