With GREAT care, and a little thin screwdriver, lever out the chrome frame surrounding the frosted glass.
It's best to go round and lever a little in several places, rather like you would with a tin of paint.
Go very gently.
Place your other hand underneath, as they can pop out unexpectedly, plus the glass is not fixed to the surround, so they can part company.
The lamps are capsule lamps and the fitting (when you've taken off the cover) should have the rating on it.
Either 10W or 20W, but be careful not to overload the transformer.
EDIT:
On second glance, I'm not 100% they are that type.
If you look on the other side of the panel into which they are mounted, can you see the fitting?
If you can take some further pics of that or wiring or transfomer (if visible and fitted) then we should be able to ID it.