[ThomasG]

Sometimes its enough to change a bulb.

Itbis possible not to push the bulb fully in into its seat, and therefore it will sit at wrong angle.

But also- bulbs are made to certain tolerances.
The coil inside will sit slightly differently in each bulb, even a pair from the same box will have these at different position.

Easy to check- just go to your nearest place that sells car bulbs, grab a box ir two (preferably clear plastic box, but that's most of them anyway) and have a close look.

Absolutely enough to throw the lights settings off.

And therefore it makes sense to at least check your beams elevation against a wall after each bulb change..