I have very little heat, how do I fix the problem?

First, if the engine seems to take forever to warm up, you may have a stuck (open) thermostat. Replacing the thermostat would help get your engine to warm up quickly and maintain the proper running temperature of about 180 deg F. This would solve your heater woes.

However, if the engine warms up normally but the heater just doesn't seem to put out, check the heater inlet valve. This valve is usually next to the firewall on the engine side and is activated by cable(s) or vacuum lines. It is common to find that the valve cables have frozen, the cable ends have broken off, or the vacuum lines are disconnected or broken. Another common problem on vacuum run valves is that the vacuum diaphragm that operates the valve has failed. The diaphragm won't "hold a vacuum" meaning that it leaks and won't operate the heater valve.

If all that seems to work okay. The heater core could be getting warm coolant through it but the underdash heater air handler box has a movable door inside that is not in the requested position. These doors are operated by cables or vacuum lines---so same checkout as above.

You may need a new thermostat if its stuck open or the heater core is plugged up and needs replaced or flushed.