To Download a Video that you already have Uploaded, all you need to do is click on the Ellipsis (3 Dots) to open up the sub-menu. You can then select 'Download Video'
A new window will appear and you will be able to choose which resolution you want to download the video in:
NOTE: The 'Download Now' button should work as intended for Google Chrome and Safari Internet Browsers. However, Internet Explorer and Mozilla Firefox may have issues with the button working. To work-around this, right-click the 'Download Now' button and Save the Link to download the video.