1. Go to Application Server Control for your Middle-Tier

  2. In the System Components section, click on "HTTP Server"

  3. In the General section, click the Restart button

  4. When asked if you want to proceed, click Yes
Alternatively, you can use the command line: 
  cd /d C:\ora\mt\opmn\bin
  opmnctl restartproc process-type=HTTP_Server