After verifying that your warranty is still active (here: Determine if Your Product Is Still Under Warranty), you need to directly contact Intel Customer Support to initiate the RMA process (you cannot do this through the forums). Here are pages where you can lookup contact information, including local/country phone numbers, by geography:
You can use the online forms service or email, but I actually recommend calling them directly. The above links provide local or toll-free numbers in most countries and support most local languages. You could also use the chat service (start here: Intel Customer Support Chat), but understand that this service is offered in English only and is subject to the normal (9:00-5:00 M-F) office hours in the Pacific (UTC-8) time zone.
Hope this helps,