.XLR and .XLS are two different document formats for saving spreadsheet files. .XLS is generally associated with the Microsoft Works application suite while .XLR is associated with both Microsoft Office/Excel and OpenOffice. Unfortunately, these file types are not immediately interchangeable, so you will need to use a program to convert between the two formats.
Download conversion software from a freeware source, such as R&L Software. (See Resources 1 & 2 )
Run the completed installer file and install the program to your local hard drive. When the installer has completed, run the finished program.
Run Excel. The conversion program should now appear as a toolbar at the top of the Excel window. If the toolbar does not appear, run the program titled "RemoveWksBars.xla" under the "Start Menu" program folder for the converter program and then restart Excel. You can now freely convert and open files in Excel using this toolbar.