Of course after developing a success full embedded product the next step would be making upgrades to compete favorably with new products in the market. Well making upgrades would require making adjustments in the sketch and Uploading it onto already made prototypes to cub the costs involved in by the hardware of a remotely located prototype. How can one upload a sketch from his location on to the prototype without going there psychically to upload through the port?
Battery powered devices need a system where the device checks over Internet connection (WiFi, mobile) if a new firmware bin file is available on a specific location on a server. If the bin file is available the device can download it and apply.
One option how to apply the new bin is to use SD card and SD bootloader (Zevero avr_boot) The sketch saves the downloaded file on SD card and resets the MCU. The SD bootloader then loads the binary from the SD card to flash.
Other option if enough free flash memory is available is to use the InternalStorage object from ArduinoOTA library. It uses the upper half of the flash memory to store the uploaded bin and then activates a modified Optiboot to copy the bin to run location and reset the MCU.
First you have to establish communication between Arduino and your computer. This communication could be wire (ex. LAN) or wireless.
Like Juraj said, you could use ArduinoOTA with an additional WiFi or Ethernet module on your Arduino, as long as arduino is connected to the network and you know its address. I haven't tried it yet, so I don't know its reliability. Even so, it helps your problem