How to replace a case insensitive string in objective-c iphone?

NSString *myString = @"select name SELECT college Select row";
[myString stringByReplacingOccurrencesOfString:@"select" withString:@"update" options:NSCaseInsensitiveSearch range:NSMakeRange(0, [myString length])];
output: @"update name update college update row";

If by case insensitive you mean the lower case replacement, Ken Pespisa has your answer, but if case insensitivity is about your search string you can do this:

[mystring stringByReplacingOccurrencesOfString:@"searchString" withString:@"replaceString" options:NSCaseInsensitiveSearch range:NSMakeRange(0, [mystring length])];

for more info see documentation of:

- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target withString:(NSString *)replacement options:(NSStringCompareOptions)options range:(NSRange)searchRange;