You can’t update hub firmware manually. If you have connected it to your account and it hasn’t updated after 24 hours… you may want to follow the guide in the following thread –> https://community.smartthings.com/t/troubleshooting-smartthings-hub-2018-and-aeotec-hub/298332
What firmware is currently showing for the hub?
btw… it is 50.xx or higher that supports hub replace.