By Rich Hall updated on 04/07/2016
You can select the HDR mode you prefer in the top menu bar of your iPhone's Camera app. Choose HDR On or HDR Off if you want to control whether to take a photo in HDR or not; select HDR Auto if you want to let the iPhone's camera determine whether HDR is appropriate.
You can also choose to compare HDR images with non-HDR images by going to Settings > Photos & Camera, and toggling Keep Normal Photo on. Now the HDR and non-HDR versions of a photo will be saved to your album.