How to update functionalities of a live Laravel web application?

I have a Laravel application. It's live and have daily users. I need to update some features. Not only front end work. Have to change back end too. With database. The problem is our old developer created this site. Now he's not here, and also no any documentation or blue print available. I downloaded the project. I can change front end even it's live. Changes affected. Is there any way to change some back end and database when it's live ? Is that a risk ? Please guys don't give minus points to this question.