Changing 727 driven gear ...

I need to change the driven gear on a 727 transmission as I recently changed the speedometer cable and the speed reading is off because of a rear end gear change and larger tire size. Found the right gear replacement (40 tooth) and a new one is being delivered today from Mancini's. I've never replaced one before and understand it's fairly easy but I can't find any videos / info on how to do it. Any advice, instructions, etc. from anyone experienced would be most appreciated. Thanks!