There are two easy ways.
The way I was taught:
1. Make 1/8 a decimal by dividing 1 by 8 (Numerator by denominator.), leaving you with 5*.125=.625, or 5/8.
The ACTUAL easy way:
2. Make 5 a fraction by putting it over 1, giving you 5/1*1/8, leaving you with 5/8.