the round cover bit should be attached to the filter and pull it out in one piece.If you haven't had the filter out for a while they do what yours has done.sometimes you have to break the inner filter bit out and buy a new one but just depends how badly scaled up it is.In theory the filter unscrews and pulls straight out!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix washing machines.