Changing the app's version

• Open app/build.gradle or build.gradle (Module: app)
• You can find some line which looks like this

  defaultConfig {
      ...
      versionCode 1
      versionName "1.0"
      ...
  }

• Replace versionCode with your app's version code (e.g: "2.0")
• Replace versionNumber with your app's version number (e.g: 2).