NSMutableArray от NSArray

У меня есть следующий код, и я хочу использовать массивы NSMutable вместо NSArray could you tell me how to load the NSMutable array, as the current method does not work.

-(void) whatever{
NSData *htmlData = [[NSString stringWithContentsOfURL:[NSURL URLWithString: @"http://www.objectgraph.com/contact.html"]] dataUsingEncoding:NSUTF8StringEncoding];
TFHpple *xpathParser = [[TFHpple alloc] initWithHTMLData:htmlData];
NSArray *titles  = [xpathParser search:@"//h3"]; // get the page title - this is xpath     notation
TFHppleElement *title = [titles objectAtIndex:0];
NSString *myTitles = [title content];

NSArray *articles  = [xpathParser search:@"//h4"]; // get the page article - this is xpath     notation
TFHppleElement *article = [articles objectAtIndex:0];
NSString *myArtical = [article content];

i have tried :

NSMutableArray *titles  = [xpathParser search:@"//h3"];

but it does load the values?