How do I update firmware on GS724Tv4?

I feel like I'm going mad, but I just cannot see an uption to upgrade the firmware anywhere in the webUI, and when I try the Smartwizard tool it doesn't find anything (I've tried on my laptop and wired desktop). I've also SmarControlCentre and that finds it on the network, but no option to update firmware in that. 

Any idea how I update it? It's currently on 6.3.1.19 but I had an email from Netgear informing me of how to update it, but when I click on the links it just refers me to the manual, and there's nothing in the manual about how to do it either! Gah!

Thanks