Those sizes will fit just fine. I have that set-up.
Also, going with the Hankook V12's isn't really an "upgrade." Price isn't everything, but the Hankooks are almost half the price of the Advans. That's why most people choose them. Relativelly good tires that won't empty your wallet. If price isn't an issue, RE-11's are top notch.
Example: 245/45/18
245 is the Section Width in mm. (unmounted)
45 is the Aspect Ration (ratio between sidewall height and Section Width)
18 is Wheel Diameter in inches