How to remove grids?

To toggle the grid on the system map:

go to the empire options - either use the crown button or the Shift+O (the oh not the zero)
look down the list until you find "system display" - about half way down. When you click on it, options will appear on the right. Uncheck the "show system hex grid" when you do not want to see it, or check it when you do. It is that simple.

To toggle the grid on the combat screen:

I forget what the screen in called, but it is accessed through the Shift+1 key combination. This brings up a dialog box - only one option. "Show combat grid". Just like the system hex grid option - put a check in the box if you want to see it, or remove the check box if you do not want to see it.

Enjoy!