How to change filter behind motor?

My son accidentally used the vacuum on a liquid. I cleaned out everything immediately including the prefilter but there is an odor coming out when I use the vacuum. I'm guessing it's from the black filter at the back of the motor. How can I remove it for cleaning or replacement?

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 2
crwdns2934285:0crwdne2934285:0