Changing API level Android Studio

When you want to update your minSdkVersion in an existent project…

1. Update build.gradle(Module: app) – Make sure is the one under Gradle Script and it is NOT build.gradle(Project: yourproject).

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)

For beginners in Android Studio “Sync gradle button” is located in
Tools -> Android -> Sync Project with Gradle Files “Rebuild project”
Build -> Rebuild Project

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.