Although there isn’t a menu item to rename your presets in Adobe Camera Raw in Photoshop, you can simply rename them in the operating system. Your Camera Raw Presets are located here:
• Win (user)/Application Data/Adobe/Camera Raw/Settings
• Mac(user)/Library/Application Support/Adobe/Camera Raw/Settings
If you are on a Mac running Lion, the Library menu is hidden by default. To reveal it, hold the option key down while selecting the “Go” menu in the Finder.

I’ve had good luck renaming, deleting, and so forth (on my Win7 machine) in:
(user)/AppData/Roaming/Adobe/Lightroom/Develop Presets
(or …/Export Presets, etc.)
… or in
(user)/AppData/Roaming/Adobe/CameraRaw…
Save some effort for those using Windows
Put In the run dialog box
%appdata%\Adobe\Lightroom\Develop Presets