Add entry to the mutable dictionary

[mutableDictionary setObject:@"VALUE" forKey:@"key"];

Add entries to the mutable dictionary from another dictionary

[mutableDictionary addEntriesFromDictionary:anotherDictionary];

Set entries for the mutable dictionart

[mutableDictionary setDictionary:anotherDictionary];

Remove object from the dictionary

[mutableDictionary removeObjectForKey:@"key"];

Remove all entries from the mutable dictionary

[mutableDictionary removeAllObjects];

Remove multiple entries from the mutable dictionary

[mutableDictionary removeObectsForKeys:[NSArray arrayWithObjects:@"One", @"Two", @"Three", nil]];