To set the admin account password use the command line utility:
./iguana --set_admin_password <password>
This will create an admin account if it does not already exist with the password specified. If the admin account already exists it will update the password.
In either case, the admin account will be updated to ensure that it contains admin privileges, by making sure the description contains #admin as part of it.
To see the changes you may need to restart IguanaX. This can also be done from the command line:
./iguana --service restart