How do I tighten it?

 

Pop off armrest console (clips along each side, no need to remove shift knob), rotate to side. You'll see an adjustment screw on a cable. Tighten or loosen this to adjust. If you are on a safe hill, you can check whether or not it works the way you want it to

 

Don't overtighten it so that it drags! I can't remember anything except that you're supposed check and make sure that it dosen't drag. I think the service manual actually has you do it with the wheels off the ground to check for freeplay/drag. Also I remember reading something like "the parking brake should be fully engaged in 9-13 clicks". I need to do this too.
If open the console up consider greasing the ball of the shift lever with Honda Super high temp Urea grease at the same time. It is actually supposed to be done annually, but no one including the dealer does it. good luck.

EDIT: I see it's an MY06, your shift lever is dosen't even need grease yet.