If the HDD is in the bottom slot then you'll need to remove the PSU and the logic board before taking out the drive sled and unscrewing the four drive pins. Another option, though, is to leave that drive in place and use the top slot for the new drive. You will need another drive cable, though.
I managed without removing the logic board or disconnecting either the fan or the antenna plate. Like others, I found it fiddly getting the new hard drive pins to line up with the holes in the case (especially with the logic board still in place) and the antenna plate didn't want to go back without a lot of fiddling about.
