If you want to replace this webpage with your content you could simply create a Webpage Redirect topic when logged into the webclient as "admin" and set its Redirect Alias to / and let the Redirect Target URL point to any of your existing resource.
As a developer of a DeepaMehta 4 Plugin you could do serve your page here through calling the WebpagePluginService from your Plugin implementation:
WebpagePluginService webpageService.setFrontpageResource('/web/index.html')
Note: This does not affect webpages you already published. They are available under their respective web alias, e.g. http://www.domain.xyz//my-web-alias.
The curent development here is that there is not yet an automatic index of all your pages, except that one in JSON.
This is mainly due to keep up all possibility for you and other plugins to register their own frontpage with the dm4-webpages plugin.
Enjoy web-publishing with DeepaMehta 4!