I'm not exactly sure what you mean by slow, or why you would want to slow it down, but their is a game speed option. However, the default is slowest so unless you accidently increased it somehow it won't help to much. If you're wanting more time to issue orders and stuff, you can hit the pause button (only against AI obviously) and the game will completely pause and you can still do pretty much anything you can while it's unpaused.
