Thank you. My other 300S is RWD with 245/45R20 . Can I switch for 275/40R20 with stock rims?Hard to say for sure without knowing what wheels you've got on there now. As far as I know, they could be either 7.5Jx19 or 8Jx19 with a 24mm offset (RWD) or 7.5Jx19 with a 55mm offset (AWD).
Either way, I think you'll find that a 285/45R19 is too large. Generally speaking, that size tire requires a minimum 9" rim width, and even if it didn't, you'd almost certainly have interference issues.
You might be able to get a 255/50R19 on there if all the stars align, but I definitely wouldn't go any larger than that. Check with the manufacturer of the tire you're interested in, but usually a 255/50R19 will have a 7" or 7.5" minimum rim width.