I have a similar unit, I have spare bulbs on board so agree with other posts that it is replaceble. But on investigation I found that the plastic rim had aged and was very rigid. I suspect I need to supply some heat to get the bulb unit out from under the rim.
I had one of those. It was a sealed unit. Took it into a motor factors and they said it was a tractor light. Cost me a couple of quid for a new unit about ten years ago.