How do I add a download button on Revolution Slider?

Outcome: I am trying to create a button on the revolution slider which will allow the visitor to download an image as a file (Its a voucher for a free dance class).

1. I can add a text link on the rev slider which downloads an image (Download Voucher)
2. But when I add a button, I can only create a link to another page and Im not able to download the image.

You can see on the slider on the page I have a button and a link.

The page I need help with: [log in to see the link]