How can I change my iPhone's camera's resolution?
Go to Settings > Camera.

You can select resolution and FPS for video &amp; slo-mo. However, you cannot change the photo resolution.

You you will also be able to choose between high efficiency, using HEIF/HEVC, or most compatible, using JPEG/H.264. This does not directly affect the resolution, but does affect how large the photo and video files are.