Downloaded the file linked by the OP onto my PC. Plugged the phone into my PC and selected "USB External Storage" mode on the phone. Two external drives showed up on the PC -- an 8GB drive and a 16GB drive. Obviously the 16GB drive was the external SD card -- the 8GB is the internal storage and you definitely don't want to put the file there. Dragged and dropped the file (without renaming it) directly onto the 16GB drive. Made sure to "eject" both external drives before I unplugged the phone.
After unplugging the phone from the computer, I selected "About Phone " from the phone's Settings menu, then selected "System Updates." It did it's little "searching for updates" thing, and BAM! It found the update and all I had to do was follow the prompts. Took about 5 minutes (it did *SEEM* to lock up for a minute there, which did kind of concern me, but I just let it do its thing and it turned out OK. Just be darned sure the phone is plugged into the wall-charger before doing this -- my battery said it had 40% before I did the update, and after the reboot it was down to 5%! Imagine if it had run out of battery power -- I'd have a brick right now!).
Anyway, it's now running 5.5.893 and everything seems to be good. I guess I'll know after a few days of usage, whether or not the radio and camera issues are fixed. (Those are the only two issues that have really caused problems for me -- I don't use wired headphones, and I rarely use the internal speaker, so I've not had any of those issues crop up for me.)
I'll post an update after a couple of days...
L.
