Need to make old Invoices / Credit Memos Zero

Hello all,

We have a business requirement that there are some old Invoices / Credit Memos in the system, these invoices / Credit memos are accounted and not made any payments against this.

We want to make them as Zero / Cancel. but want at the same time we are worried about accounting.

So please suggests us the correct way to cancel them.

Thanks,

Abhijeet