You have to download kingo root apk.
Step 1: After downloading Kingo root.apk on your phone copy the app to the internal storage of your Xiaomi Redmi 4A.
Step 2: Open the file manager that you are using on your Xiaomi Redmi 4A and browse the Super-root.apk that you have copied to the internal storage of your phone.
Step 3: Now install the Kingo root apk on your device. Once the app gets installed, you will be able to see the app in the apps drawer.
Step 4: Make sure that you are connected to the internet. Choose a strong internet connection like WiFi or 3G connectivity.
Step 5: Now open the Kingo root app from the app drawer of your device.
Step 6: The rooting process will not take much time. The process will be completed within 1-2 minutes.
Step 7: Once the rooting process is completed in your Xiaomi Redmi 4A, Reboot your device once.
Note: If KingoRoot fails to root your Xiaomi Redmi 4A in the first attempt, no need to worry, keep trying 10 – 15 times. This is because KingoRoot downloads only one script for once.
Or visit my thread for further info..or check mi forum..