Cannot use /setmaxplayers command in a non-cheats world version 1.7.0

It affects 1.7.0 (i chose 1.8.0 because 1.7.0 was an invalid version, anyway i can use commands like /w and /me, but not /setmaxplayers. I used to be able to use that but now it says CHEATS ARE NOT ENABLED ON THIS WORLD. Plz fix. Thanks