Generator of cyclic groups $Z_{pq} $

Question

Instead of asking to find the number of generators of $Z_{pq} $ where $p$ and $q$ are prime numbers it was asked to find generators of $Z_{pq}$. This is to find the number s which are relatively prime to $pq$. Is there any method to find all numbers relatively prime to $pq$ ? I know $1,p, q$ and $(pq-1)$ will be relatively prime to $pq $ .But these are not the only numbers relatively primer to $pq$ . All multiples of $p$ and $q$ less than $pq $ will not be relatively prime to $pq$ . but it is not enough
Can we generalise this question ? that means can we find all numbers less than a particular number $n$ and relatively prime to $n$.