I want to convert an older xls file to xml. I can save it as that but it
doesn't display properly. What can I do?

Depending how much data there is in it, I would open it up, create a
new document in the latest format and then copy and paste from the old
to the new (or write a VBA proceedure if there was a lot of Sheets).
Once you have the data in the new spreadsheet, save it with a new name
then try to export as .XML
That should help clean it up and may solve your problem.