My Dyson DC 15 Animal appears to have a lower filter but the manual makes no reference to this filter. I sits right underneath the dust bin. Is this a filter and if so how do I change it?

Hi and welcome

Yes, that will be the post motor filter. It's mainly there to collect the carbon which comes off the contacts in the motor. Dyson claim it's a lifetime filter but if your machine is worked really hard for a long time you might improve the suction a bit by replacing it. Unless you're having problems I wouldn't worry about it though as it is unlikely to make much difference (and if it does need replacing then that's a good sign that your motor is near the end of it's life and you'd be better off replacing that).

Or just try washing it, that works on most Dysons.