The wrapper to your header has the class "top-bar-sticky". You have javascript in your simple_theme_functions.js file that is running a function on this class to make it sticky. You can simply comment this out and it should work.
Just wrap it in /* CODE */ to comment it out. Also you can remove it but that isn't best practice for purchased templates since you essentially bought that piece of code.
There are many ways to make this effect happen, so there are many ways to turn it off and they all depend on how it is turned on. Could you sharea a page link for us to look at?
The wrapper to your header has the class "top-bar-sticky". You have javascript in your simple_theme_functions.js file that is running a function on this class to make it sticky. You can simply comment this out and it should work.
Just wrap it in /* CODE */ to comment it out. Also you can remove it but that isn't best practice for purchased templates since you essentially bought that piece of code.