Change Transmission Fluid - 2000 Chevrolet Blazer

Drain the Transmission Fluid and Replace the Filter
Raise, support and level the blazer on jack stands or ramps. Place a drain pan that can hold at least 4 quarts of fluid beneath the transmission.
Employ a socket wrench to remove the retaining bolts on the fluid pan, except for the two on either end. Loosen the two bolts on the lower end of the pan. Gently pull down on the edge of the pan so that it separates from the transmission case. Let the fluid drain. You may need to tap the pan with a rubber hammer to separate the pan from the case.
Remove the last four bolts and the pan when the fluid finishes draining. Loosen the bolts a little at a time, allowing the remaining fluid to drain. Clean the pan and the magnet inside.
Scrape the old sealant from the pan flange with an appropriate scraping tool. Do the same on the mating surface of the transmission case.
Remove the filter, Look for the filter and the O ring between the filter and valve body and remove it.
Install the new transmission fluid filter and gasket. Place the new gasket on the mounting flange of the fluid pan. Replace the fluid pan on the transmission and tighten the bolts to 165 inch pounds with a torque wrench. Return the Blazer to the ground.
Replace the New Transmission Fluid
Pour 4 quarts of ATF fluid into the filler tube using a funnel. Start the engine and let it idle for a minute or two. Apply the parking brake and the service brake. Move the gear selector through the gears and stop at "Park" or "Neutral.
Add enough fluid to bring the level to 1/8 inch below the "Add" indicator, if needed. Let the van run for another 10 to 20 minutes to allow the engine and transmission to reach a normal operating temperature
Check the fluid level again to ensure it reached the "Hot" indicator on the dipstick. Add more fluid if needed and replace the dipstick in the filler tube. Turn off the engine.
Good luck and hope this helps. Note the 4X4 wire harness bracket needs to be removed and just place it out of the way and if you have a cell phone, just take a picture of it before you disconnect it so you have a reference on how it goes back together.