Modify, test the library in Android Studio from GitHub

I use for example library Sweet Alert Dialog. I want to modify this library by adding text size customization to library/src/main/java/cn/pedant/SweetAlert/SweetAlertDialog.java.

public SweetAlertDialog setTitleText (String text, int size) {
         mTitleText = text;
         int height = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, size, getResources().getDisplayMetrics());
         if (mTitleTextView != null && mTitleText != null) {
             mTitleTextView.setText(mTitleText);
             mTitleTextView.setTextSize(height);
         }
         return this;
      } 

Now I want to test this library and use it if it does what it should do. I need that one time explanation to get it. At the moment GitHub is a little bit confusing.

UPDATE

I have added this library via

dependencies {

    compile 'cn.pedant.sweetalert:library:1.3'

}

Is there any way to just make your own compile path and test it? After branching the library or so?