First you convert both of the fractions into improper fractions:
10 1/2 = 21/2
5 2/3 = 17/3
Then you times the fractions by the other fractions denominator:
(21*3)/(2*3)= 63/6
(17*2)/(3*2)=34/6
The you can take the numerators away from eachother and place them over the denominator:
(64-34)/6 = 29/6
Then you take out as many 6's as possible from the 29 and you have that number before the fraction and the remainder as the numerator:
4 5/6
Hope this helps! :)