This is, unfortunately not possible. It's a major process to convert the finished project into the code necessary for your site to appear online (which is why X5 is chosen, for those of us who do not know how to code) and this can't be reverse engineered. It's vital to regularly back up your site using the Export function. I then transfer these backups (using a NAS) to a backup hard drive.

What you can do is use the images and text from your site online (copy and paste) to recreate the site using X5. This takes time, but you already have all the words, images and layout available to you and it's much easier than starting from scratch. You can probably make some improvements along the way. The Pro12 version that your profile suggests you are using is pretty old but still relatively functional unless you want to start doing E-Commerce or something like that (even the latest version isn't ideal for this but that's another debate...)