If you bought simpleContact Pro from CodeCanyon.net you can get the latest version by logging into your account and downloading the application.
If you bought it from this website, you can get the latest version by going to this page:
http://www.simplecontactform.com/support
Enter the email address that you used to purchase it, and you will be emailed a new download link.
The current version is 2.1. See the release notes for information on the changes, and the updating guide for instructions on how to update your installation.