Many webhosts don't make Enhanced Disk Caching available in certain hosting environments, ie Shared Hosting or Managed WP Hosting. VPS or Dedicated may afford additional opportunities.
First, contact your host at make it's available. If it is, they can install it for you to the server (if you have managed hosting.)
If not, you can see if an OpCode cache is available, or you will have to use Basic Caching.
