Using the GitHub GUI, how do I make a .sh file I have created in my repo into an Executable File?

I use the GitHub GUI to do my work. I created a ,sh file in my repo. How do I make it become an Executable File, as per the image below? 

Or, must the terminal be used to make the new file executable?

There isn’t a method to change a file’s attributes via the web interface. You’ll have to use a local copy of the repository to make the change.

I hope that helps.