Adding to Stiggy100 statement
You will need also change the Admin/invoice.php for complete Edit of the information,
You will need to Edit this lines the following located on line 164(this could change)
<td class="dataTableHeadingContent" align="right"><?php echo TABLE_HEADING_PRICE_INCLUDING_TAX; ?></td>
<td class="dataTableHeadingContent" align="right"><?php echo TABLE_HEADING_TOTAL_EXCLUDING_TAX; ?></td>
Hope this helps



