How to update version number of react native app

I am using React native with Android. How can I update version number in the app? As I am getting this error.

I am generating file as per this url https://facebook.github.io/react-native/docs/signed-apk-android.html

I have tried modifying AndroidManifest.xml file, but after I build it, that file gets automatically modified back.

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.facebook.react"
    android:versionCode="1"
    android:versionName="1.0">

Here, I modified the XML:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.facebook.react"
    android:versionCode="2"
    android:versionName="1.1">

After, build file automatically changes back.