Where is a heater core in a 1993 Chevy Beretta?

The question you ask is too involved for a proper answer. You need to go to a car parts store, and get a repair manual for your car. They cost about $16.00 Or, go to a Public Library. i had to change the heater core in my 93' beretta. its under the dash in the middle. there are three panels to you can take off: under the steering column, behaind the heater controls and stereo, and one under the glove box. you want to take off the panel behind the heater controls. there are a couple things to take off before you can see the heater core and it is hard to put it all back together afterwards. and onother thing, dont loose any of the screws, there are quite a few of them. good luck