Separate mouse click with button click

I have a tank and some button to change shell type the player wants to use. I am using GetKeyDown(Mouse0) to fire shell. However, when I click on the shell change button the tank will fire and i do not want that to happen. What is the best way to seperate button clicks from normal mouse clicks ? I am relatively new to Unity so any detailed answers or tutorials are greatly appreciated. Thanks in advance!

This should help