OK well I took it apart. Three screws in the base then some careful wiggling. The hard bit is releasing the clear plastic glow panel. The buttons just pop out - though be careful here too. I undid the clips at the top of the unit (4 tabs) and eased it forward - this seemed to help them out. Once the buttons are out the housing for the lamps can slide out of the main housing. This has two spring tabs that you can squeeze and pull it with.

The bulbs appear to be LEDs and are soldered and glued in place so not exactly a simple swap.

Something strange - mine only has three lamps where I'm sure it should have 4?

Apologies for the low quality photo - my digital camera has gone UTS and used my phone.