'08 135i speaker upgrade with NAV

[MIAblu1]

Hey guys, I've read a few posts about people upgrading their speakers and underseat woofers but haven't come to find a direct answer to my question. I have an '08 Year one of the 1 with the original pop-up NAV and was wondering what would be needed in order for me to be able to upgrade the under seat woofers? I don't believe I have an upgraded syste unless the NAV package includes an upgraded sys but I do have the tweeters that are mounted in the side view mirror spots so I'm guessing maybe I have the Mid level sys?
Anyway, I'd like to upgrade the two woofers and maybe even the tweeters with Alpine speakers but was wondering if it'd requiring coding and such and also what are the exact measurements of the speakers that I'd have to order in order for them to be direct fit to the stock spots? Any info is greatly appreciated