Here are a few examples to get you started

http://[your domain name]:[your password]@dyn.dns.he.net/update?hostname=[your domain name]

Autodetect my IPv4/IPv6 address:
% curl -4 "http://dyn.example.com:password@dyn.dns.he.net/nic/update?hostname=dyn.example.com"
% curl -6 "http://dyn.example.com:password@dyn.dns.he.net/nic/update?hostname=dyn.example.com"

edit the /etc/inc/dyndns.class file.

change dyndns.class file to:

case 'he-net':
              $needsIP = FALSE;
              log_error("HE.net: DNS update() starting.");
              $server = "https://dyn.dns.he.net/nic/update?";
              curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
              curl_setopt($ch, CURLOPT_USERPWD, $this->_dnsHost . ':' . $this->_dnsPass);
              curl_setopt($ch, CURLOPT_URL, $server . 'hostname=' . $this->_dnsHost);
              break;

https://dyn.dns.he.net not normal update ipv4 address.  I think should use  % curl -4 https://dyn.dns.he.net  or use http://ipv4.dyn.dns.he.net