Finally... Something I can answer around here. boge513 please disregard the extremely shortsighted response that Danger_Mouse spouted about as that kind of response will surely get you into a very cumbersome situation!
I updated 3 of the Epic's floating around work to EB13 by removing their 16GB cards and inserting a smaller 512MB card that contained only the update.zip file. Afterwards reinserting the original 16BG card without the update cause no ill effects.
In short, you may remove the update.zip file from your Micro SD card after successfully installing the update.
Sorry... I couldn't stop myself. Just playing!