You will have to use appropriate software. You can even do it on your own but it takes work and you probably won’t do it properly.
You need to test normal and overrated load until the server no longer responds. The ideal is that the normal load (or slightly above what can be considered normal) is running for a long time (24 hours or more).
Just this is not enough, you need to try to simulate realistic scenarios and try to create unusual situations forcing the application or server to have problems in unclear situations.
They’ve already done a list software for this.
Apache itself comes a utility for this called ab (Apachebench).
If you want something more sophisticated and can use Java Apache itself forwarded the project Jmeter.
They say that the httpperf HP works with more intense loads if necessary.
Another is the Dummynet.
I’ve heard good things about Seagull.