I Have A Problem In Speech, ( I Am 48

I have a problem in speech, ( I am 48 years old). A doctor told me that the problem is due to more gap between upper teeth and lower teeth due to protruding upper teeth. The doctor said that the problem in speech is due to escape of air from the extra gap.
Can you please advise me how to reduce the gap between upper and lower teeth?
Ejaz Hussain, from Pakistan