I have a Nikon d40 with a 200mm lens I use to shoot my 12 year sons sports pictures at night with a dimly lit outdoor field.. I have read the posts about using an iso1600 with a shutter speed of 2.5

Please explain how to do this on the camera. I typically use the green automatic setting and during the day I use the Running icon on the wheel.
I now you have to use one of the manual setting but do not know how to set it up.

Thanks
Joe g