You can put this solution on YOUR website!
Interesting question. You factor the number. Look at the factors you found. Can you factor any of them? If so, do so. You keep factoring the factors until there are only primes.
Finding the factors of numbers is a skill, mostly. You look for obvious divisors (is the number even? is it a multiple of 5? is it a multiple of 3? etc.).
Algorithmicly you divide the number by all numbers less than or equal to its square root and check for remainder of zero.
There are a number of rules for checking if a number is divisible by some other number (these are called divisibility criteria) but this is beyond the level of help you will want here.