You can change the default priority that an application runs with by starting it with the nice command, but if you want to change the priority of a process that is already running, the command to use is renice.
Renice can be used to change the priority of a single process, or of all the processes owned by a specified user. As with the nice command, the priority values range from -20 to +19 and negative numbers raise the priority of a task while positive numbers lower it. Only the superuser can specify negative numbers (thus raising the priority of a process).
Link: New Linux User
Tags: Linux