The devices of the D8xx series (e.g. D862, D865) differ in many aspects of hardware and software. Among other things, the devices of the D8xx series have a dual firmware partition. This means that if you want to perform a firmware update on a device of this series, the phone will not restart directly (and then first download the firmware and finally install the update) as in the previous series, but it will load the update during operation and only then restart.
Right-click on the link to copy the link to your clipboard
Open the phone web interface, and navigate to the menu item "Maintenance/Software Update."
Insert the copied link into the text field and press load to start the download.
The screen will light up briefly, you will get a message in the display that the update process has been triggered and the phone loads the firmware file in the background and unpacks it.
This should usually take less than a minute.
After the download has finished, the phone simply restarts, and you can move on working with the new firmware after a few seconds.