How To Remove Duplicate Applications in Mac OS X
Removing Repeat App Entries in "Open with"
Open the terminal application
Copy and paste the following coding into the terminal application, then press enter
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user
Now relaunch the finder, go back to any file and right click on it with the 'open with' option and you will se all the duplicate entries gone.
If you are not comfortable using the above procedure, you can download a third party app called Twins. Twins is an application that will hunt and kill all duplicate files on your mac, the advantage of using this application is that it has options to scan and select specific files to keep.