After I added more memory to dynatrace managed server form 32 GB to 48 GB, Then I need to modify -XMX -XMS in dynatrace manage server for add more heap, Can I modify it ?
You cannot, dynatrace is allocating available memory automatically (with reservation for each components). You have to know that there is not only Java server, but elasticsearch, cassandra nginx etc as well. All of those components has to have resources available. This is why it is possible that dynatrace is not using all available memory on host.