This is an english translation of http://www.guideitech.com/apple/come-rinominare-facilmente-un-gruppo-di-file-su-os-x-yosemite/ While I translated it mostly to practice my Italian, it's a great article and shows a cool feature on Yosemite if you don't want to deal with doing this at the command line :) Also please let me know if you find any mistakes or bad translations!
I’m sure there are hundreds of unorganized files on your macs right this moment. Vacation photos, PDF documents, downloads, TV series, or whatever. The first step in organizing these contents is to give them proper names.