Yes it's quite easy job .... plus you can take the chance and sound proof also the doors (there are couple of threads for this in the forum )
It took a specialist about 1 to 2 hours to change the speakers front and rear ...including the tweeters offcourse ...using size speakers that fit at the door cards no one can really tell any difference ...rather only by sound .. which is much better ... honestly ..if you are not in to much with the bass then you don't really need a sub ...offcourse for the extra bass ..if that's what you are looking for ..you will need the sub....
Saying this ... I think by having the beats ...which already has all the cables installed ( amplifier and sub ) then by changing the factory speakers which is as said just low to normal quality speakers with something more premium ...will make a clear difference at the sound ...but even with the factory system me personally by just changing the speakers as mentioned before ...and sound proof the doors ...it made a difference ... and fir me it's more than enough as I just like to listen clear and not loud music ... but each one to their taste ..