For access to the AP via SSH the user name is root and the password will be the same as the console password specified in the AP system profile. This is also where you can disable SSH to the AP if needed.
The modify the AP system profile for a particular AP group, go to Configuration ->AP Groups, select the desired AP group. On the right side you will see the tab "profiles", click on it and expand the profile tree to see the AP system profile. AP Console Password is in the "Advanced" Section.
Please keep in mind that default profiles should not be changed. If you modify the Console Password you should save the changes under a new meaningful profile name.