Need a little more info using Filters 'After'

How do I do that in the 'after' function though?  How do I update the $response to edit the body?  Do I use a 'return' statement?  Call a function on the $response object?  I can't seem to find an example anywhere of how this would work for here:

Code:

public function after(RequestInterface $request, ResponseInterface $response)
{
  // how do I manipulate the $response var?
  // do I need to return the $response var or anything?
}