Drain the antifreeze. Keep the drain pan under the heater core hoses.
Disconnect the battery. Remove the hose clamps/ 2 hoses fom the heater
core from under the hood in the engine compartment. These hoses are hard
to reach. You can try to reach the hose clamps from under the raised car.

Inside the car: remove the center console if you have one (there is a
little clip to pry out from the front of the trans-shift lever), heater
ducts and covers and the square black plastic heater core cover. You will
need various small sockets.

Then just snap the 2 straps loose and replace the core. Make sure that the
hoses are not the source of the leaks. Replace the hoses if they are old.
One of the hoses is 3/4" on one end and 5/8" on the other end. So, you
will need a hose size adapter in the hose if it not a factory hose
assembly. I dont remember the size of the other hose.