You can power off the machine. Otherwise, you can just use the computer. The operating system manages the details, and there is nothing you can or should try to do to upset that. Do you obsess over the number of processes, the clock frequency, the cooling fan RPM, etc? No? Then forget about memory use too. I'm seriously.
When you open an Activity Monitor session, in the memory pane, keep an eye on the "memory pressure" graphic; it's best to be in-the-green. Also find out/monitor what's using large percentages of your RAM, and determine if that usage makes sense.
thanks for the answer. I am not in trouble with the Performance but i cant exchange my SSD and the newer iMacs are not easy to open for exchange. The Problem is new with sierra. Before i didnt have this Problems.