I don't know specifically for redis, but for servers in general:
What OS or distribution? Often there will be a stop or /etc/init.d/... command that will be able to look up the existing pid in a pid file.
You can look up what process is already bound to the port with sudo netstat -nlpt
(linux options; other netstat flavors will vary) and signal it to stop. I would not use kill -9
on a running server unless there really is no other signal or method to shut it down.