To build a new SITECON model call the Tools->SITECON->Build new SITECON model from alignment main menu item. The following dialog will appear:

<center>
     <br>
     <img src="/wiki/download/attachments/8094111/Building new SITECON Model.png"/>
     <br>
</center>

Here you need to select a nucleotide alignment and an output model. Optionally,  you can change other parameters. After that click on the Build button.