What is rejetting?

Well, I did several searches. I can't find exactly what I'm looking for. I hope this thread is helpful to others with the same question.

I bought a set of Cobra Speedster Shorts, A K&N air filter, and a KURYAKYN Pro R Hypercharger. All item will be here this week. I hear that I will need to "rejet" when I add this stuff. Ok, so here are my questions that I've come up with:

1. What exactly is rejeting?
2. Do I need a "rejet kit?"
3. Is this job something I can do on my own or do I need a professional?
4. I've heard talk of a "pair valve removal" Do I need to do this too? Is this part of the procedure?

If there is anything I'm missing or need to know please let me know. I'm looking to install this stuff next week.

Thanks in advance!
:choppersm