To make all the characters in a String uppercase or lowercase:
let text = "AaBbCc"
let uppercase = text.uppercaseString // "AABBCC"
let lowercase = text.lowercaseString // "aabbcc"
let text = "AaBbCc"
let uppercase = text.uppercased() // "AABBCC"
let lowercase = text.lowercased() // "aabbcc"