If there is a new firmware available for your lamp Casambi app will inform about it with a pop-up screen. You can also check if there are updates available in Nearby Devices screen.
Nearby Devices screen can be accessed from More tab. In Nearby Devices screen tap the ‘Check for updates’ button. If there are updates available you can see an arrow in the corner of the lamp icon. Tap on the lamp you want to update and select ‘Update firmware’. Tap on the ‘Start Update’ text. Once the update is done there will be ‘Update succeeded’ text in the screen.