How to adjust paid invoice?

Hi gurus,

To help understanding the issue, I give an example issue below,

I have an Invoice with total amount is 1000.

This invoice is already paid 850 and fully accounted in the last period.

Now, I want to adjust the invoice total amount to be 850 same as the paid amount.

The problem is I do not know the right procedure to do the adjustment.

Please advice.

Thanks,

Andi