There are a couple of situations every week where I have to convert files from one format to another. So far my go to site has been ZamZar but I recently learned about another player called CloudConvert. Like Zamzar, CloudConvert is web based which means no installation, constant updating and worries about configuration.
CloudConvert supports the conversion of 140 different filetypes. and using it is wonderfully simple. You visit the site (which is responsive so it works on your smartphone too), select the file, choose the format to convert to and allow it to send your converted file to Dropbox / GoogleDrive.or be emailed when the conversion is completed.