You can still use the Lync client user interface after you apply this update for Lync 2013 (Skype for Business). Get the general information about how to switch between the Skype for Business and the Lync client user interfaces for Office 365 users and Lync Server 2013 users.
Or else if your already with Office 2013 you can update by few clicks
Go to Outlook/File/Office Account and click Office update
Then you can experience new Skype for Business UI after the restart