How can i take the heater core out?

Before resorting to replacing the heater core, first verify that the thermostat in the engine is operating properly. Sometimes the thermostat will stick in the open position. When this happens, the coolant does not get hot enough to provide sufficient heat. Also check to make sure that the heater core is not clogged up with rust or other debris. You can do this by disconnecting the heater hoses from the heater core [done from under the hood]. Place a garden hose against the upper metal tube and turn on the hose. Water should come out the lower hose without a lot of restriction. If debris or rust comes out with the water, flush the heater core out, using the hose, until there is no debris and no restriction in the heater core.
Replacing the heater core is a big job. I would suggest that you entrust this to a pro, unless you have lots of experience working on cars. The video linked below gives an outline of what is involved. See

Changing Heater Core in 1999 Dodge Dakota

There is a tap or valve on the heater or hose that controls the hot water to the heater radiator, make sure this is working and not closed or broken.

i had to have the heater control panel replaced when mine stopped working.

Check the resistors on the same blower circuit, or heater core?

remove the radiator cap, leave it in park, start up and let it idle. turn on the heater so the air gets out of the heater core. give it 15 or 20 min. after it reaches operating temperature. if needed, do it again. also remember your thermostat may be bad

If the heater core isn't leaking it doesn't likely need changing. It sounds like you could have a problem with the heater control valve - a valve in one of the heater hoses that controls flow through the hose. If you smell coolant and see moisture on your windshield (inside) or have coolant leaking onto the floor - you might need the heater core replaced.

this repair is very extensive if you have limited ability then do not attempt,,,,,, the steering column has to be dropped. entire dash removed, ac freon recovered coolant drained below core then the heater box assembly has to be removed as a whole then disassemble heater box to replace the core then reverse procedure.

not a job for the faint of heart. picture the whole dash board, right up to the windshield sitting on the seats,that kind of gives you an idea. no fun to do. the dealer gets about 8 hours for the job