You have three options.
1. Uncheck the checkbox before clicking "update now" (see below)
2. Don't immediately upgrade, after 30 days you'll get this update silently (and without any third party software) if you have "Check for updates automatically (recommended)" set in your Flash Player control panel.
3. After receiving the notification update, close that dialog and download one of the stand alone installers from here: http://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-windows.html#mai n-pars_header
Hope this helps,
I had the same question. I did not get a choice to not install Chrome and Google Toolbar - there were no checkboxes - it just started installing and then I saw that it was installing all 3 and I stopped it. The page you mention doesn't take me to a page where I can download just Flash.