To enable gzip, login to cPanel account for the user account which GZIP compression wants to be turned on. Then click on Optimize Website under Software / Services. Choose Compress All Content or Compress the specified MIME types to enable GZIP compression on all websites hosted by the particular account. Click on Update Settings when done.
Once you’re done you can easily test to see if the compression is working by using the gzip test tool here: http://www.gziptest.com/