First of all you need to download the file from here https://gradle.org/releases
unzip the file and copy folder something like this gradle-3.3(if version is 3.3) and past it to C:\Android\Android Studio\gradle
Now open the Android Studio and from the left top corner Open File > Settings > Build,Execution,Deployment > Gradle
Now give the the path of folder gradle-3.3 in Gradle Home