Changing API level Android Studio

For Android Studio users:

1. Right click the App directory
2. Choose the "Module Setting" (F4) option
3. Change the ADK Platform as what you need
4. Click OK

Gradle will rebuild the project automatically.

---

Update 2022

1. Right click the App directory
2. Choose the "Open Module Settings" (F4) option
3. Change the the minSdkVersion in the Default Config tab
   NOTE:
   You might also want to change the targetSdkVersion in the Default Config tab and
   the compileSdkVersion in the Properties tab
4. Click Apply, then OK, and Gradle should automatically be synced.

When you want to update your minSdkVersion in an existent Andriod project...

1. Update build.gradle (Module: YourProject) under Gradle Script and
   make sure that it is NOT build.gradle (Project: YourProject.app).

An example of build.gradle:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    buildToolsVersion "28.0.2"

    defaultConfig {
        applicationId "com.stackoverflow.answer"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}

dependencies {
    androidTestCompile 'junit:junit:4.12'
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

2. Sync gradle button (refresh all gradle projects also works).

or

3. Rebuild project

After updating the build.gradle's minSdkVersion, you have to click on the button to sync gradle file ("Sync Project with Gradle files"). That will clear the marker.

Updating manifest.xml, for e.g. deleting any references to SDK levels in the manifest file, is NOT necessary anymore in Android Studio.