I have POS devices that is based on linux OS and have a firmware running on top of it. We can write programs using the vendor given SDK using C and run on these devices. I want to develop a system that can upgrade this program version remotely. Replacing the binary executable file of the program with the new binary file is enough.

Is there any developed platforms for this?

Is using SCP is reliable and secured?

scp is fine to use. First develop a way to upgrade it with one file which does the actions you wish it to, then determine the best way to transfer your file to the system remotely. If the vendor who provides the SDK doesn't have an upgrade process illustrated for you to use then you're going to have to design one yourself. There likely is not a developed platform for this because it is embedded Linux. Typically I just write a startup script which detects the presence of an upgrade archive file, then performs the upgrade prior to booting.