refactor js php html codigniter code

One of previous developer did for us invoice tool in codeigniter view file. All functionalities are working now fine.
Used ajax to write data to database. Codeigniter general framework. lot of different variables added to code. i want to refactor that code to usable and then needs to add more functionalities there. needs clear that code. add comment. and change format to DRY(Dont Repeat Yourself). Needs merge repeatedly elements. Needs remove unnecessary code if have