How to rename a file in Mac OS X

It’s not obvious how you can rename a file or folder in Finder, but is very simple, just KISS (Keep It Simple, Stupid)

In Finder, open the folder with your file in it.
Find the icon for your file. Click once on that icon then click and hold the mouse button down on the filename below it for a second or more.
After about a second of holding down the mouse button the text will become editable and you can type over the filename.