Listbox Scrollbar customization in WPF

I'm making an application for being used in a touch screen. One of the forms shows a listbox with scrollbar activated that is a little bit tricky to use by touching the screen with fingers.

I have tried to make an style that makes bigger buttons inside the scrollbar but I can't apply it to a listbox.

Is it possible to make a style for make bigger buttons in a scrollbar inside a listbox?

Thanks

From stackoverflow

• If you are using Blend then you need to:

  1. Right click your ListView
  2. Select "Edit Control Parts --> Edit a copy"
  3. Now right click the ScrollViewer in "Objects and Timeline"
  4. Select "Edit Control Parts --> Edit a copy" again
  5. Now you're editing a template for the ScrollViewer and you can play
     with the size of the VerticalScrollBar
  

  If you're not using Blend then you are just creating a Template for the ListView that refers to a new Template for the ScrollViewer.