Resources

According to our contract with our client, We should not exceed 200 (men) resources at any given time. However when i extract information from Primavera to do my resource Histogram I get more than 200 (men) resources. If i get more than 200 (men) resources i must level these resources to be less than 200 (men) resources. My problem is how do i level these resources on my schedule? in my schedule i have a completion milestone which does not move as it is a constraint. so how do i level these resources?