You have a multiple options:
First, you can use kill. But you need the pid of your process, which you can get by using ps, pidof or pgrep.
ps -A // to get the pid, can be combined with grep
-or-
pidof <name>
-or-
pgrep <name>
kill <pid>
It is possible to kill a process by just knowing the name. Use pkill or killall.
pkill <name>
-or-
killall <name>
All commands send a signal to the process. If the process hung up, it might be neccessary to send a sigkill to the process (this is signal number 9, so the following examples do the same):
pkill -9 <name>
pkill -SIGKILL <name>
You can use this option with kill and killall, too.
Read this article about controlling processes to get more informations about processes in general.