Text only install IMG for Sangoma Appliance

We have a FreePBX 50 that came with FreePBX Distro 12. I’d like to wipe that install and put 13 on there. Is there a special way to install the distro on these boxes? I loaded the IMG from the site but the install menu doesn’t pass through the RS232 redirect. Couldn’t find anything in the manual that shows how to install from scratch.