If coolant is leaking from the heater, the radiator is leaking and needs to be replaced.
You will need a Phillips screwdriver.
1. Disconnect the wire from the terminal «minus» battery.
2. Remove heater (see «Removal and installation of a heater»).
3. Turn out three screws of fastening of a radiator..
4.... and remove the radiator from the heater housing.
5. If the radiator is very dirty, clean it with a hair brush and blow it with compressed air. Replace leaking radiator.
6. Install the radiator in the reverse order of removal.