Renaming a folder in Mac OS X is very easy, and theres a few different ways you can do it.
Rename a file or folder by selecting it and hitting the return key just click on the icon of the file/folder and hit the return key, then type in the new name.
Rename a file or folder by selecting it and clicking on the filename with your cursor after you have selected the icon, click on the actual filename text and hover for a moment, then you can rename the item.