As you work to shape your Animal Crossing: New Horizons island into the form you've always desired, some of your early choices may come back to haunt you. You're forced to hurry through some early moves, and sometimes don't even have a more varied option later in the game. This is true of bridges and inclines, which are necessary for exploring other parts of the island and attracting new villagers. Due to the fact that this often unlocks some of the more essential features, players often rush through this and find themselves having to make changes later. This raises the question of what to do with the old material. In Animal Crossing: New Horizons, is it possible to upgrade bridges and inclines?
If you mean literally, is it possible to upgrade a lower level bridge or incline, such as the log bridge, to one that looks better? Not at all. If a bridge or incline is in service, it is permanently in that configuration. You cannot pay the difference to exchange one for another, which means that if you're going for the zen bridges or brick inclines now and wish to exchange one of the earlier ones you put, you're out of luck. However, not entirely, since there are other ways to handle this case. They simply cost a great deal of time and Bells.
Rather than updating, you're almost forced to replace them. You can pick a bridge or incline for demolition by speaking with Tom Nook in Resident Services. This will occur the next day, so ensure that you are comfortable with not using the bridge or incline for an extended period. Confirm with him that you want it demolished and then wait for the job to be completed. If completed, you can upgrade it by simply replacing it with a new one that more closely matches the aesthetics you've developed for your island.
Thus, while the precise answer to the question of whether you can upgrade bridges and inclines in Animal Crossing: New Horizons is no, there is a way to accomplish the same mission. However, you must pay the full price again, which can be inconvenient. There are many other ACNH features you can't change as well.