How to make all characters lowercase in NSString?
NSString has a cunningly named lowercaseString method.
NSString *noCaps = [yourString lowercaseString];Edited to add
If you are asking how to change the actual string to be lowercase - you can't. NSStrings are immutable. They can't be changed after they have been created. If you want to change the string in place you should use an NSMutableString like so:
[aMutableString setString:[aMutableString lowercaseString]];