How do I change out the blown Kenwood speaker in the back?

You may need to remove the rear package shelf inside the back window to access the speaker if you can't get to it from the trunk. This usually requires removal of the back seat.

dude u shoulda let me kno u have a blown speaker is it on the rear deck?

I dont' think you have to remove the seat, but you'll have to remove the entire back shelf. Should be 4-5 bolts and the thing should just come down. I'd get somebody to help you, though. It's kind of akward and heavy.

Here is some good news... There are no speakers in the rear deck! That's right. Our cars came with 7.1 system. 2 tweeters in the rear mirror pockets, 2 in the front doors, 2 in the back doors, and 1 subwoofer. So before you go removing parts you don't need to remove, check out the space where speakers are supposed to go from the trunk area... you'll see them MIA! You're welcome.

If you're talking about the kenwood sub, it is enclosed with the molding and amp. If it's under warranty, Mazda will replace the whole thing free. If it's not, I would either take it out or go to a third party to take care of it.

LOLll sorry :P its the eaasyest thing you could do on a mazdaspeed pro .. just remove the sub protector ( a litle round grill ) its not that hard to remove , and than remove the 8 screw ... disconnect the wire , connect the new sub ( around 40$ for a good 8" ) screw it back , and than enjoy the sound ;) = 5 min job

are you absolutely sure its blown or is it just making a really weird rattling sound everytime it thumps? if thats the case its jsut your amp rattling around back there. msp forums give a solution of installing some foam between the amp and whatever its rattling on. solves the problem easy.