How you manage to change all desiggn of your Android application to material design ?

There are many things to take into consideration. I'll list a few that I follow;

1. Read the official Material design guidelines carefully

2. Look for compatible libraries from GitHub for widgets, animations, graphics etc. so that you can still target most of the Android devices out there in the market and not increase the Minimum SDK requirement for your app.

3. Take inspiration from the standard Google team apps like Inbox, Calendar, Clock etc.

Its the age of flat designs in the design industry. Google played well and they were smart enough to introduce boldly in the market. Using flat graphic icons is a way to change all design of the android app to material design

it's very easy. you don't need to change design of android application. but use existing material and design user define library from the internet and change your self.