Microsoft originally imposed a deadline of May 13 on consumer users to move to the Windows 8.1 Update. On May 12, Microsoft announced a deadline extension to June 10.
Business users still have until August 12 to move to the Update for Windows 8.1 and Windows Server 2012 R2. Microsoft extended the deadline for those updating using Windows Server Update Services (WSUS), Windows Intune, and/or System Center Configuration to update users' machines. Microsoft execs unveiled the new deadline in mid-April after outcry from some that Microsoft wasn't giving them enough lead-time to apply the update.
Consumers running Windows 8.1 who have Automatic Updates turned on don't need to do anything; they should have received the Update automatically via Windows Update by now.