Clear multiple entries form "Open With" context menu [duplicate]
Solution 1:
You need to reset the Launch Services Database
Use the following command in the terminal:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user
Wait until the terminal returns you to a prompt. You should now be all set.
My understanding is that this will work in anything from 10.5 and up.