You can do this by implementing your own title bar. In order to do so set your window style to none:
WindowStyle="None"
This will mean that the window will have no control box (minimize, maximize, and close buttons) and you will need to implement your own.
You can take a look at the following links to get you started:
http://blog.magnusmontin.net/2013/03/16/how-to-create-a-custom-window-in-wpf/
http://www.codeproject.com/Articles/140267/Create-Custom-Windows-in-WPF-with-Ease
http://www.kirupa.com/blend_wpf/custom_wpf_windows.htm
How can I style the border and title bar of a window in WPF?
Good luck