I need to upgrade my App in Google Play

I own an App in Google Play: [login to view URL] I want it to be upgraded with new content and with new logic I have 1500 articles, each article has to be displayed one by one only one article should be shown every day user can read previous articles by selecting previous days I do not have the source code for this App its simple, 2 Activity app Same App should work in website as well, you can use Angular or React JS for this