UserDefault

To reset the NSUserDefaults to the standard values use:

[NSUserDefaults resetStandardUserDefaults];
[NSUserDefaults standardUserDefaults];

If you want to delete every key use the following:

NSDictionary *defaultsDictionary = [[NSUserDefaults standardUserDefaults] dictionaryRepresentation];
for (NSString *key in [defaultsDictionary allKeys]) {
    [[NSUserDefaults standardUserDefaults] removeObjectForKey:key];
}
[[NSUserDefaults standardUserDefaults] synchronize];