To change your host code, click on Account > Account Access. Click on the 'Actions' button that corresponds to the code you wish to change. Select "Change Host Code" from the drop down menu and confirm your choice in the popup.

You may also change your host code within 'My Conference Settings' within the drop down list of your avatar found in the upper right corner of your profile. Click on the 'Change' link and confirm if you would like to change your host code.