Require login for download - Joomla site

I have a page on my site where users are allowed to download a file. Right now anyone can download the file, I need to change this so that only logged in users are allowed to download. If they try to download the file and are not logged in it should take them to the log in screen and give the message "You must login to download files. Click here to register." The words 'Click here to register.' will link to the registration page. To view the download link go to: [login to view URL] then double click on an item in either models or datasets. Then click on the 'download' link at the top. This change needs to be made for both the models and datasets tables on the site. Let me know if there are any questions.