Please check the watch version firstly, then find your watch version, download the patch file according to your watch version and copy it to the file folder in the watch, and then do the steps in watch as follows:
Open the "Settings" - "About smart watch" - "System update" - "Local upgrade" - "Internal storage",
choose the patch file and click it, it will upgrade automatically.
Highlight: For watch version which is 20180831 backwards, please burn the firmware to the latest version "20200226" directly. Here is the download link for the guide on how to burn the firmware:
Note:How to check the version in watch: click the "Settings" – "About smart watch" – "Build number" which is the watch version.