How I update gradle manually in Android Studio 3.0.1 :

Remind you when you upgrade Android studio up to Version 3.0

You should ungraded Gradle and Android gradle-plugin!

Currently Android Studio 3.0.1 using Gradle-4.1 and  Android-gradle-plugin 3.0.1

Find gradle folder inside your project

Open gradle-wrapper.properties and change

distributionBase=GRADLE_USER_HOME

distributionPath=wrapper/dists

zipStoreBase=GRADLE_USER_HOME

zipStorePath=wrapper/dists

distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip

Open root build.gradle file and change in buildscript

buildscript {

    repositories {
        mavenLocal()
        mavenCentral()
        jcenter()
        apply plugin: 'eclipse'   

     maven {
            url 'https://maven.google.com/'       

     name 'Google'   

     }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.0.1'    }
}

allprojects {
    repositories {
        jcenter()
        maven {
            url 'https://maven.google.com/'  

          name 'Google'        }
    }
}