To change an xlt (Excel 2003) template to an xltx (Excel 2007) template the following steps need to be followed.
Run your existing Excel 2003 report out as normal in Excel 2007
Minimise Excel 2007
Go back to Report Manager and unlink the xlt template from the report by selecting the Unlink Template icon
Confirm that you would like to unlink the template
Notice that there is now no Template linked to your report
While your report is still selected, select the Create and Link icon
Select the Workbook to link as Template (the Excel workbook you’ve minimized) and select OK
Confirm that you would like the Parameters on the Second Worksheet by selecting Yes
You will now be given the option to select the Template File Format
Select the Excel 2007 Template (*.xltx) and select OK
Select OK again
The new template is now successfully linked to the report
