Go to Dashboard and hover with mouse over slider image.
Click EDIT to enter the slider and open up it's settings.
Open slider settings from Dashboard
That will lead you to Slider settings page. If you look at the "breadcrumb navigation" on the top, you'll see exactly where you at (for example: Dashboard > Slider > Slide 1).
On Slider settings page you'll see menu on the left side (Slider settings). Navigate through menu to edit global slider options like navigation arrows, pagination type, sizes for devices, preloader, etc.