Hey,
jep, seems like they have edited this page in the last three years sometime…
If you check this readme in the WIO LTE repository from seeed there is a basic description about how to upgrade the firmware: https://github.com/SeeedDocument/Wio_LTE#software-updates
I’m not sure if it’s a good idea to use the firmware provided by the hardware manufacturers instead of the published firmware from seeed provided here: http://www.espruino.com/binaries/ (I think the one to use are the espruino_#v##_Wio_LTE.bin ones, the latest seems to be espruino_2v09_Wio_LTE.bin, uploaded 2021-04-19)
Hope this helps you a bit
Edit: nearly forgot that back then I created an issue regarding to the firmware flashing process, there is a litte bit more information about how I was able to set the board in DFU mode on a Windows PC: https://github.com/SeeedDocument/Wio_LTE/issues/1