I have some falken hanabis , they are all 18x 7.5, i need new tires for it but i dont know what size to get. right now i think on the front is 245/35/18 and for the rear i have 245/45/18, i dont think these are the right sizes and i know its not the staggered fitment, i just got the car and the guy left those rims and tires on it.

 

215/40/18 front and 245/35/18 rear would be proper. I'm not quite sure those sizes you said are the right sizes if there are on the s2k already. Double check the tire and see what it says. Pics help too.

 

Even the 245/35R18 is going to be stretched on a 18X7.5 wheel. I would say that the 215/40R18 is the correct front size.
If I can help with the tires let me know.