First, make both mixed numbers into improper fractions.
8 1/3 = 25/3 and 6 2/3 = 20/3
Since you have a common denominator, all you have to do is subract the numerators, so 25/3 - 20/3 = 5/3
You can keep it in improper fraction form, or go back to a mixed number.
5/3 = 1 2/3