Starting a new change while one is in progress

[eluser]Unknown[/eluser]
I'm working a "Pull Request" currently. I want to start
another change but when I look at the "Contributing to
CodeIgniter" document I notice:

One thing at a time: A pull request should only
contain one change. That does not mean only one commit,
but one change - however many commits it took.

How to I handle that? I suspect that I fork
BillHeaton/CodeIgniter but wanted to ask before jumping
off the cliff. Be gentle, I'm still very new at github.