Not able to convert XLS file to XLSM file in Excel 2013

Hi Experts,
I have recently installed EXCEL 2013. I am not able to convert XLS file which contains Macros to XLSM file. When I am trying to save through ‘Save As’ option it is not saving the file. The file still remain in XLS format. Even after I have changed the name no new file is creating in XLSM format.
I don’t know what is the problem with it.
Can anybody gone through these type of problem.
Please help me.
