problem updating app on google play

Good morning, I have an application that I had uploaded to google play, but recently I made changes and improvements, and then, I uploaded it to the play store. all that by changing the gradle and the code version correctly. However, when I see the application in play store, in a cell phone that had already installed an earlier version, it does not come out "update" only "install" (although the new version that I put it) comes out. What would be wrong?

- graddle -

apply plugin: 'com.android.application'

android {  
    compileSdkVersion 23  
    buildToolsVersion "23.0.3"  
    defaultConfig {  
        applicationId '************'  
        minSdkVersion 19  
        targetSdkVersion 23  
        versionCode 3  
        versionName "2"  
    }  
    buildTypes {  
        release {  
            minifyEnabled false  
            proguardFiles getDefaultProguardFile('proguard-android.txt'),   'proguard-rules.pro'  
            debuggable false  
            renderscriptDebuggable false  
            renderscriptOptimLevel 3  
            zipAlignEnabled true  
            jniDebuggable false  
        }  
        debug {  
            debuggable true  
        }  
    }  
    productFlavors {  
        Newapp {  
        }  
    }  
}  

dependencies {  
    compile fileTree(include: ['*.jar'], dir: 'libs')  
    testCompile 'junit:junit:4.12'  
    compile      'org.jbundle.util.osgi.wrapped:org.jbundle.util.osgi.wrapped.org.apache.http.client:4.1.2'  
    compile files('D:/AndroidStudio/Newapp/libs/ksoap2-android-assembly-3.5.0-jar-with-dependencies.jar')  
    compile 'com.android.support:appcompat-v7:24.0.0'  
    compile 'com.android.support:support-v13:24.0.0'  
    compile 'com.android.support:design:24.0.0'  
}