you wouldn't. This issue is more akin to a webserver not being configured for the latest mime-types.
Since Office 2007~2010 and Vista~Windows7 is new, a web server isn't going to know what application runs what file extension.
You will need to contact your host. They will need to update their mime types.
in lieu of this you could try and create an .htaccess file in root and add to it
application/vnd.ms-word.document.macroEnabled.12 .docm
application/vnd.openxmlformats-officedocument.wordprocessingml.document docx
application/vnd.openxmlformats-officedocument.wordprocessingml.template dotx
application/vnd.ms-powerpoint.template.macroEnabled.12 potm
application/vnd.openxmlformats-officedocument.presentationml.template potx
application/vnd.ms-powerpoint.addin.macroEnabled.12 ppam
application/vnd.ms-powerpoint.slideshow.macroEnabled.12 ppsm
application/vnd.openxmlformats-officedocument.presentationml.slideshow ppsx
application/vnd.ms-powerpoint.presentation.macroEnabled.12 pptm
application/vnd.openxmlformats-officedocument.presentationml.presentation pptx
application/vnd.ms-excel.addin.macroEnabled.12 xlam
application/vnd.ms-excel.sheet.binary.macroEnabled.12 xlsb
application/vnd.ms-excel.sheet.macroEnabled.12 xlsm
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xlsx
application/vnd.ms-excel.template.macroEnabled.12 xltm
application/vnd.openxmlformats-officedocument.spreadsheetml.template xltx