@Jorge-Sosa-0 There are some devices which originally came with ASA firmware which could then be upgraded to FTD - a good example is the 5506-X which was originally ASA, but can be upgraded to FTD (as long as it's a new enough version with an on board SSD). I don't think devices which were always intended as "true" Firepower devices can be downgraded though (to be honest, I don't think there's a lot of reason you'd really want to?) Nonetheless, if you have one of the "transitional" devices with FTD and you want to downgrade, I think that should be possible - once you've swapped the image over, you're running ASA.
I've got the opposite problem - my 5506 has ASA firmware which I really want to update to FTD, just for lab use - but it's proved impossible to get the image I need to make the upgrade, the only way seems to be to get a service contract for the device, which is quite a lot just for a lab - but even if I swallow the cost it's so freaking complicated to get organised! I wish there was a way to buy just a single image for lab use!
Not meaning to hijack your thread, but while were on topic if @ronnie-wong or @anthony-sequeira have any suggestions on a way to get hold of an FTD image for 5506-X I'd love to hear it!