Add option to add video to an existing custom Wordpress page template

General information for the website: Ballroom dance classes
Kind of development: Customization of existing website
Num. of web pages/modules: 1
Description of every page/module: Template name: 'Class Detail'
Description of requirements/features: I currently have options to add an image and a quote to the left side of this page when I'm populating the template with my own data. I need also to add the option for me to upload a video instead of an image, either from a YouTube URL or directly from my computer. I think this is a case of adding an additional custom field, I am just not sure how to do that myself.

URL: www.latinballroomlondon.co.uk
Example of existing template: http://www.latinballroomlondon.co.uk/beginners-ballroom-classes/

Please contact me if you need any other details to confirm the addition is possible.

Thanks,

Gemma
Extra notes: