change heating radiator

[demal]

Hello, the heating radiator in my polo does not work. I have to change it but the mechanic it want to charge me a ton of money that I don't have to do the job. I was wondering if someone can point me toward a guide to change it myself. do I have to disassemble all the dashboard or can I reach it in some other way? like from beneath? thanks in advance for anyone that could give me some advice.