Clicking with the right mouse button on a process in the process list or process tree will pop-up a little menu that allows you to send certain signals to this process or change it's scheduling priority. The latter is not available on all operating systems. Changing the priority will affect the amount of CPU time the process will receive to do it's job. As a normal user you can usually only increase the value which will decrease the priority. The higher the value the less likely the process will get CPU time. This can be used on systems that are shared by many people. Longer running jobs (batch jobs) should be "reniced" to preserve a short response time for interactive processes.