Once you remove the volute (clear part) you need to carefully remove the oring from behind the pinwheel. After you do that, you can use a screw driver to carefully pop out the impeller just enough for you to be able to grab it by hand and pull it.
Just pride the impeller from behind the pinwheel with the screw driver, a little bit at a time on each side just enough so you can grab and pull by hand.
Regards,