Changing invoice numbering through 'Invoice options' only applies to new or future invoices. Once an invoice is created, one should not change its number by editing it. As this may create linking issues with any applied payments for the invoices, any applied credit notes or bank checks, etc.
One option is to delete the invoice, and create new. Before creating new, change the numbering in Options->Invoices to what you wish.
[Edit: I just saw your other post]
So, if you want to use same invoice details to generate new invoices multiple times, editing invoice number won't help because it won't generate second invoice for you. Having said that, there are few ways to generate multiple invoices:
- Use recurring invoice feature if your invoice needs to be generated strictly on periodic basis (weekly, monthly).
- Otherwise, create a quote, never delete it and convert that to invoice every time you need one.
