How to kill a running process
Open the Terminal
Type: ps aux and press enter.
long series of processes will appear in your Terminal.
look for the application you want to kill
find that process, you can see a PID number, example 3225
Now kill that process, type: sudo kill -9 process number (replaced ‘process number’ with the actual number) and then press enter.
example sudo kill -9 3225
resource : How to Kill a Running Process