What's your model?
The updates can be queried:
Code:
http://data.onyx-international.cn/api/firmware/update?where={"buildNumber":0,"buildType":"user","deviceMAC":"","lang":"en_US","model":"Poke3","submodel":"","fingerprint":""}
(This is technically not a valid URL but your browser knows how to turn quotes into %22.)
This is for the Poke3, insert your model.
In "downloadListUrl" it will give you the URL of the .upx file.