We are developing software with Nordic nRF52840. Please tell me how to update applications using Bluetooth, such as "Reprogramming" and "Flash Bootloader", and sample programs.
DFU (device firmware upgrade) can be achieved with the use of the BLE secured bootloader. You can follow the very precise and detailed documentation of the SDK to :
1 - Try the example project from the SDK and understand how secured DFU operates 2 - Adapt the example to your use case
There are really two types of DFU, one with user interaction (the press of a button for example) the other is the buttonless DFU that only needs the advertising functionality to be enabled.
A good staring point could be this application template. There are many steps to make the DFU work with your own secured keys and I recommend you to read carefully the documentation to avoid any difficulties.
Pro tip : Next time, try not to express your needs in the post title ;-)
