Refresh/update my Web-site

I would like to update the [login to view URL] web-site for a dental practice: to give it a 'modern' look, make it more user-friendly, make mobile devices friendly, add extra content, make it a bit bigger and so on. I am open to your suggestions. It's a simple static web-site developed with a simple stack of Web and Microsoft technologies: HTTP, CSS, JavaScript and ASP.NET (for requests over e-mail form). It's very fast and easy to maintain (I'm hosting it by myself) and I would like to keep it as it is.