You can test if you have the latest flash here
Download Flash Player
I would personally remove Flash from add remove programs, and forget about that site.
Flash Player is integrated with Internet Explorer in Windows 10.
You do not need to install Flash Player.
If you are using Windows 10 and browsing the web with internet explorer you cannot download a version for that just Chromium , opera and Firefox
If the website is asking you to install flash player I would be very Leary of installing it from their site
Some virus scanners will block Incredimail (Norton)