It's a simple one, converting NSString to NSDate we use NSDateformatter using dateFromString method. We need to provide the Dateformatter style with existing style for NSString
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ssZ"];
NSDate *date = [dateFormatter dateFromString:@"2013-02-01T06:25:47Z"];
NSTimeZone *pdt = [NSTimeZone timeZoneWithAbbreviation:@"PDT"];
[dateFormatter setTimeZone:pdt];
[dateFormatter setDateFormat:@"HH:mm:ss zzz"];
[dateFormatter setDateFormat:@"K:mm a, z"];
NSString * updated String = [dateFormatter stringFromDate:date];