How to change the currency for an invoice?

[Yee Koon Loh]

Hi,

    I am new to GNUcash. I am currently using version 1.8.8 from Mandrake 10.0.

   1.  I have created an invoice in SGD$. But, I discovered that it
should be in US$ instead. How can I change it to US$?
   2. If I cannot do that, how can I delete the invoice and reissue a
new one? I need to delete the old one as I need to keep the invoice
number the same for accounting purposes.
   3. It seems that the currency is tied to a particular customer. How
can I issue invoices of different currencies to the same customer?

thanks

yee koon