Your shed has a nice ridge vent and you've got a good window as well as the screened opening. i don't really see that you need any more ventilation, but you could always add a few vents like these up on the walls if you felt you needed to. They even make them that would fit your octagon window. Of, course, you would have to take the window out. https://www.lowes.com/pd/Accord-Ven...-x-6-in-Outside-13-73-in-x-7-74-in/1000161133