Say, for example, you have an improper fraction (it usually is if you're trying to convert to a mixed number) like: 55/7 You would take the highest number that is divisible by the denominator, which in this case is 7 (7x7=49; 7x8 would be 56 and we don't want that) You subtract the number you got (49) from the original numerator (55). That will give you 6.
Now, you put the whole number (7) before the fraction (6/7)