How to change package name in flutter?

For Android

To change the package name we just need to update appliationid in build build.gradle only

defaultConfig {
    applicationId "your.package.name"
    minSdkVersion 16
    targetSdkVersion 27
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}

For iOS

Change the bundle identifier from your Info.plist file inside your ios/Runner directory

<key>CFBundleIdentifier</key>
<string>com.your.packagename</string>