How can I convert an NSDictionary to an NSMutableDictionary?

Use -mutableCopy.

NSDictionary *d;
NSMutableDictionary *m = [d mutableCopy];

Note that -mutableCopy returns id (Any in Swift) so you will want to assign / cast to the right type. It creates a shallow copy of the original dictionary.

In case of Swift

var tempDic: NSMutableDictionary = yourDictionary.mutableCopy() as NSMutableDictionary

Try this in swift 3

let mutableDic: NSMutableDictionary =  (yourDictionary as! NSDictionary).mutableCopy() as! NSMutableDictionary

NSMutableDictionary *newInfo = [[NSMutableDictionary alloc] init];
[newInfo setDictionary:info];

Also works, since you are setting the dictionary not appending. You can also use:

[newInfo addEntriesFromDictionary:info];

for the same effect and to append to existing content.