First of all, download the new firmware from the Internet or from here:
General_DVR5x04_Eng_P_V3.200.0024.0.R.20150525.bin
https://files.ixnfo.com/Firmware/Dahua/DVR5x04.zip
The main thing is that it was not older installed in the DVR, it can be seen from the version and date of its output in the web interface.
The standard IP address of the Dahua DVR is usually 192.168.1.108, so to enter it, you must manually assign an IP address to the computer, for example 192.168.1.109.
Open the WEB interface of the DVR and go to the menu “System” – “Update“.
Click “Browse… “, select the downloaded firmware and click “Upgrade” to start the upgrade process.
When updating the firmware, you can not turn off the power of the DVR.
The update process lasted about 5 minutes, after the configuration was not reset, the admin user password was reset to the standard admin, I updated the firmware remotely.