Essentially the problem comes down to two parts
A) Enable SSL On your web server
B) Enable WordPress to Use HTTPS instead of HTTP
A) As mentioned by @gotham there are several windows clients to do this I recommend certify as it is a visual client http://certify.webprofusion.com/
B) Once you have SSL working on your web server for your site then the next step is to make the application (WordPress use HTTPS)
The best article I have read on this is this one:
Why - because the author approaches the transition in a slow and methodical matter that won’t make your site not work. There are lots of people who break their wordpress sites by trying to do everything at once
Another good article:
The theory is once you set the base urls to use HTTPS instead of HTTP all articles etc should update as they are relative to the base.
Sometimes this doesn’t happen so it’s good to have a tool that can update stragglers for you.
A good tool for automating the updating of internal links to HTTPS: https://wordpress.org/plugins/wordpress-https/