Amount in word

In sale invoice once the customers pay part payment where amount in word are not reflected the changes…

Because the original invoice amount doesn’t change.

But when we receive the he amount the final figure need to show in the invoice which is the final amount to receive.

That is not the way the Total amount in words feature works. It lists only the initial total. As you record receipts against the sales invoice, the mini-statement at the bottom deducts these from the Balance due. There is a difference between the initial total and the current balance due.

If you want something different, create a custom field and manually enter the current balance due instead of checking the box.