Steps for IPB503A-2TW firmware upgrade:
1. Copy the unzipped folder upg_ipc_hi3518eV300 to the Micro SD card
2. Turn off the camera
3. Insert the card
4. Turn on the camera
5. Wait 2 minutes
6. Remove the card (with the camera on)
7. Reset the camera
8. If the micro SD card is required for image storage, delete the update folder
The firmware with the mentioned folder can be found on the product page: