After the truck is jacked up and blocked(jack stands placed) . You need a drain pan to collect the fluid in a drain pan. Slide it towards the back of the transmission pan l .get the right size socket on a ratchet and loosen all the screws starting from the back to the front . Then remove the screws starting from the back of the pan to the front leaving 2 screws to hold the pan while you lower the back part of the pan letting the fluid drain into the drain /collection pan... After you let it drain for a few minutes then remove the last screws holding the pan and slide it out from under the truck while moving the drain pan all the way under the transmission...empty the rest of the transmission pan into the drain pan or container(used laundry detergent bottle/or a used winshield washer fluid bottle whatever you have). You will need to wipe of the transmission pan and check the gasket if the gasket is damaged in any way you will need a new(they usually need replaced so buy one before you start to save yourself some trouble)..you will also want to change the filter at the same time. After putting the new gasket on the pan relace the pan the reverse order you took it of the vehicle...after the pan is replaced put your transmision fluid back in through the filler tube on top of the engine..make sure to check the fluid level after you have dropped the truck back on level ground..(remove jack and jackstands)..after replacing the fluid check for leaks by running the motor for 3-5 minutes...that should be it....just in case get yourself a manual for your vehicle in case you don't know how to get the filter out...and always I repeat always have some one with you when working on your vehicle..for safety reasons..