Who told you to migrate to HTML5? Why? What do you want to do with HTML5 that you can't do now? What HTML5-specific features do you want to use? Obviously, this is a very broad subject (and not an Expression Web-specific question). Look in the Forum FAQ
for resources, this isn't really a topic that can be covered in a forum (especially since you provided so little for anyone to go on)Comic Sans walks into a bar. The bartender says, "Get out! We don't serve your type."
Who told you and why? If your site functions the way you want and it is working in all major browsers there is no need for HTML 5. If you are targeting mobile devices (aka iOS primarily) and you have video you may need to use an HTML 5 alternate fallback
to play them on those devices but in most cases there is no need and even some good reasons not to use HTML 5 on a website. So provide more information on what you are trying to accomplish by migrating to a not yet final HTML version.FreeExpression Web Tutorials For an Expression Web forum with without the posting issues try