here are some other 2005 helpful threads that might answer a lot of your current/future questions.

size thread

remove stuff

some entire new sound systems

just to answer your question right now,
stock front speakers: 6X9
stock rear speakers: 6.5"

when you buy aftermarket component speakers they should come with tweeters.
you need to use something thinner than 1/8" thick when mounting your tweeters. any thicker and you will not be able to put the factory cover back on.

removing your tweeters are very simple:
1) pop the cover off
2) unscrew the 4 screws holding it down(use small socket wrench w/ phillips bit OR phillips bit on vise grips)
3) pull out tweeter and disconnect wire

check your PM