One really easy way to do it is to use Automator. There are numerous ways to go about it in Automator, depending on what works best for you. One way to do it is to use two Finder actions:
1) Ask for Finder Items (with Allow Multiple Selections checked)
2) Rename Finder Items (Replace Text in Finder Item Names)
When you run it, select the items you want to change and that's it. Alternatively, you could replace Ask for Finder Items with Get Specified Finder Items and specifically drag and drop everything you want to change right into the window.
In either case, a piece of cake.