How do you replace the heater core in a 1996 Chevrolet Blazer?

Ok you have to remove your all the parts of your dash. When this step is done, you gonna see a plastic black box, remove this one (3 Screws). Under this one you can see your heater core.

When this step is properly do, open your hood. Look on your firewall (Up Passenger Side) and remove all bolts, remove the 2 heater hoses. Remove your heatercore and replace it, Redo all of this step inverse for reinstallation! Good luck!

(Sorry my english, im not the best in this language!)

But before you replace it...

If you think it may only be clogged, turn heater controls to full open/hot. Then turn off engine. Disconnect heater hoses under the hood. Connect a short hose to the "input port" to carry dirty water away from your engine. Connect another hose to the "output port." Shoot water from a hose-end sprayer into the "output" to backflush the core. My heater in 98 Blazer had quit heating. I just had to wash the crud out it it worked fine afterward. (it was going to be a BIG job to take off enough dash parts to get to the core to deal with it)