Stupid question about tyre sizes

I've always just replaced like for like when changing my tyres, but my car has got a sticker inside the door that says either 235/75/16 OR 255/70/16 (it has the 235s on currently) - can anyone tell me what, if any, difference it would make if I changed them all for the 255s? Currently tyre shopping and trying to widen my options to save a bit of money!