What he’s telling you is to look at all the processes you have running to see which one or ones is using the most resources. There are a couple of ways to do that.
There’s actually a panel in Webmin that will list the processes running on your server, how much memory they’re using, how much processor, etc.
You can also go to your terminal and type: ps aux
That will give you a list of all the processes running on the system and is part of what Joe was telling you to look at. It looks like this:
You’ll be looking for an application using up lots of system resources and what user those processes belong to. You’ll probably find, as Joe mentioned, that one person/user has a ton of apps taking up a ton of resources.
That is what you’ll have to stop.