A change of your business's details in ⚙️Settings won't alter your documents retrospectively - such action would create quite a mess in your previous documents. If your business details changed, change it first under Settings - Business details.
Then, if you need to change your business details on a specific invoice
on iPhone and Android devices edit the invoice, click on your company name, your business details appear and you can change it for the current document
on the Billdu website edit the invoice, select Edit company details. A window appears where you can edit all your company details for that specific document
on iPad - currently it's not possible to change business details on a document, please use the Billdu website or an iPhone or Android device
If you've added a logo or signature to your Business settings, it will show up on the first invoice you create AFTER such change. In case you need a logo to show up on your invoice, upload a logo to your business settings first and create a new invoice (you can also use the duplication feature)