The “software image” takes up the entire disk.
SMB appliances do have a “default” image you can revert to but it’s not meant to be accessed via the CLI.
There is a method to revert to this image (or upgrade) via the WebUI.
If you wish to replace this “factory” image, you need to boot off a prepared USB drive with the relevant image, which will also factory reset the appliance.
For non-SMB appliances, you can generally either: revert to factory defaults (done from boot menu), boot off a prepared USB drive with the image you want (reimages/resets the appliance), or follow the normal upgrade process via CPUSE/Blink to the version you desire.
You can review the relevant Install/Upgraade guide for the exact steps: https://sc1.checkpoint.com/documents/R80.40/WebAdminGuides/EN/CP_R80.40_Installation_and_Upgrade_Gui...
If you can provide your starting point (appliance type and version) and your desired state, more precise steps can be provided.