You need to associate the relevant files type(s) to the program(s) you want to open them with. It's not a difficult task but we can't provide you with exact instructions unless we know what the attachments are. Are they, for example, images in the jpeg format or perhaps something like Excel spreadsheets?
If you're not sure what the attachments are, please tell us the file extension(s). e.g. if an attachment is shown as 'mydog.jpg', it's the 'jpg' bit that we need to know about.