Make sure you have a filter wrench...they are really cheap and sometimes the filters are a pain to get off. Otherwise it is very straight foreward. Just unscrew the oil cap on the engine, then undo the bolt on the oil pan. Let it drain for a bit till it drips no more. But the bolt back in. Change the filter. Then refill to the correct level. Have fun...it might be a bit messy, but it feels good to do something yourself on the Hummer.
And normal oil as stated in the manual will work just fine.