Hi m-s-s!
First you have to create a MyiRex Account here:
https://myirex.irexnet.com/user.php
Then you take your iLiad and go to the settings.
Right on the first settings page are the MyiRex account settings.
There you enter your email address you used with the MyiRex account and the according password.
Depending on your network you need to set our network settings in the "iLiad Profiles". Just follow the wizard.
After that, just do a loong press of the upper right button and connect to iDs. Your update will be downloaded and installed automatically.
Have fun with your iLiad.