

Login to Lync again, and that should have cleared everything in the cache.

Next go to c:\users\username\AppData\Local\Microsoft\Communicator\then open your sip namefolder, and within that folder is a file called and right click and delete.

Now you can able to see all the hidden files and folders in your PC by visiting the location of folder. In the folder options window, go to View tab and check the option Show hidden files, folders, and drives under Advanced settings. In the Windows explorer, click on Organize on the toolbar and then click on Folder and search options. (the Win button has the Windows logo on your keyboard). Open Windows explorer by pressing the keyboard shortcut ‘Win+E’. You need to get to the AppData folder, but by default its a hidden folder. I understand your want to delete all the conversation history folder.
