One thread about it from a while ago is
viewtopic.php?f=20&t=6478 be sure to check out Derf's excellent video on page 2 of that thread
It's a lot easier to check the valve clearances than it is to adjust them. Adjusting requires installing shims, which you have to measure the clearances first in order to know what thickness shims you might need to order. Assuming your 04 is a base, and not a GT, I attached the section from the toyota matrix manual on valve clearance adjustment