I have a bunch of lessons about "how to strum" in the lessons section though I don't know how useful they will be with out the video.

To sum up strumming up, it is just like strumming down but in reverse. Angle your pick the opposite way from strumming down and just move your hand from your feet towards your head.

You can practice just playing the upstrokes to give a ska / reggie type feel to what you are playing!

It is also a good idea not to hold your pick to rigidly. Let the angle be determined by moving it over the strings and stop it from moving to far to get the sound you want.