When an update is available, the Roku will auto-update itself. This includes both OS and channel updates. Of course, you can manually do a update check in the Settings/System/System Update menu.
But if you're looking for firmware 9.3, be aware that Roku doesn't release it to all players at the same time. They use some internal (and unknown to the users) schedule for what players can get the update, and what geographical locations can get it as well. This way on the off chance there's something seriously wrong with the update they haven't messed up the entire world. So they do a slow, gradual rollout.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.