DevOps Optimize an Java JVM process for a Java application that runs OutOfMemory

I need your help for 1 hour to help me figure out how to optimize a Java JVM process running on a Linux CentOS machine. I've worked with the various parameters (-Xmx) but I am not getting it right. After running the process under high load I eventually get OutOfMemory, but usually the server has RAM still available as far as I can tell. If you are experienced with Linux debugging process from DevOps perspective. Please let me know an hourly price for helping me out with this.