To begin you have to find a common denominator between the two fractions. In this case that number is 8 because 4 is a factor of 8.
2/4 * 2 is basically 2*2 over 4*2 = 4/8
From there simply subtract the numerators
5/8 - 4/8 = 1/8
So 1/8 will your final answer.
