Hello, my name isXXXXX will do my best to assist you. I don't know your automotive experience level, so I may have to ask questions of you before I can answer. I only know as much about your concern as you have stated in your post, so please feel free to add as much detailed information as possible. If I cannot help I will opt out and let another expert assist you.
Here is the step by step instructions, you should be able to do this in less than 3 hours.
REMOVE OR DISCONNECT 1. Air cleaner and duct assembly. 2. Drain coolant. 3. Rotate engine forward.
4. Both heater hoses at heater core. 5. Right and left instrument panel sound insulators. 6. Rear compartment heat duct adapter bolt/screw and adapter. 7. Heater outlet duct bolts and duct. 8. Heater core cover. 9. Heater core.INSTALL OR CONNECT 1. Heater core. 2. Heater core cover. TIGHTEN ^ Screws to 3 NM (27 lb in). 3. Heater outlet duct and bolt/screws. TIGHTEN ^ Screws to 2 Nm (18 lb in). 4. Rear compartment heat duct adapter and bolts/screws. TIGHTEN ^ Bolts/screws to 3 Nm (27 lb in). 5. Right and left instrument panel sound insulators. 6. Both heater hoses and clamps to heater core. 7. Rotate engine back. 8. Refill coolant. 9. Air cleaner and duct assembly. TIGHTEN ^ Bolts to 5 Nm (44 lb in).
Then I would not attempt this repair. This is not something for a beginner, there are too many small issues for me to walk you through it over the internet.
The labor is only 2.3 hours so it would not be too much to have it done by a mechanic.