If your proforma has not been finalised, you can change it. To do this, go to the ACTIONS column at the far right of the transaction line, then on Modify.
Once sent for validation, your proforma can no longer be modified.
You can convert your proforma into a sales order by clicking on ACTIONS, then CONVERT INTO NV SALES ORDER.
The ACTIONS button also allows you to duplicate the proforma. A new proforma will be created and will have all the details of the duplicated document.