From your photo it looks like the top one uses a 472 type quartz bulb with three locating prongs and the bottom one uses a 410 type older bulb with a round fitting with one small lug sticking out.
The older 410 type is on left of photo, they are not interchangeable and both use different holding clips which should come with the head lamp.
Both headlamps should be a matching pair.
Providing every other fitting is the same you can fit the later type and use 472 bulbs which give brighter light, but only as a pair.