if you go to a smaller wheel, such as 17s for the front, you must make sure that the wheel has enough clearance for the brake calipers. The rear brakes are smaller.
Also, you will need higher aspect ratio tires in order to maintain the same (or close) overall diameter or your speedo and other speed related sensors will be inaccurate.
for the front, probably 225-45-17
rear, 245-45-17
most 17" rims are 7 or 7-1/2" wide...so 245s might be too wide for the rim.
Also the stock rear rim is 9" wide, so a 7" wide rim will need spacers or the rear will look really skinny (too tucked in)...and if the offset is too different, it could effect handling and tread wear...

IMO, the 19s on the rear is for looks...they could have in on 18's and no one would have noticed...

FYI-stock rims are
18x7.5, et35
19x9, et22