To perform a clean uninstall of Lync for Mac 2011, follow these steps:
     1.     Log on to your computer by using administrative credentials.
     2.     Exit Lync if it's running.
     3.     Drag the Lync application to the Trash.
     4.     To remove your existing Lync preferences, delete the following files:
             ◦     Users/username/Library/Preferences/com.microsoft.Lync.plist
             ◦     Users/username/Library/Preferences/ByHost/
             ◦     MicrosoftLyncRegistrationDB.xxxx.plist
             ◦     Users/username/Library/Logs/Microsoft-Lync-x.log
             *Note This file is present only if you turned on Lync Logging.
             ◦     Users/username/Library/Logs/Microsoft-Lync.log
     5.     To remove all Lync files from your computer, delete the following folders in the Users/username/Documents/Microsoft User Data folder:
             ◦     Microsoft Lync Data
             ◦     Microsoft Lync History (move to Desktop to retain previous chats)

            *Note If you delete the Microsoft Lync History folder, you delete all conversations that are saved in the Conversation History.
     6.     In the Applications/Utilities folder, open Keychain Access.
             ◦     Delete any keychains on the left that resemble OC__KeyContainer__<email address>.
             ◦     In your Login keychain, delete the <your email address> certificate.
     7.     In the Users/username/Library/Keychains folder, delete all the files that resemble OC__KeyContainer__<email address>.