Addign a youtube video

Hey guys,

Firstly let me say I am very new to wordpress so this maybe a very simple issue, sorry if it is.

I went to replace existing videos on a website I have recently been asked to work on. Our developers still have control of it but everytime I ask them a question it costs a bunch of money so I am trying to learn how to use wordpress myself.
The website is here: http://www.viclarity.com and if you scroll down to the end of the page you will see four videos. These are the ones I want to replace. I want to keep the outer light grey box with the four videos inside.

In the back of the site on wordpress I can see where the deeloper has the link for the video. He has a link in the custom field area. The name is vimeo_embed_code and the value is a number. I want to relace this with a youtube video.

When I try and put the video url like other people say in the text editor nothing happens. Can any one help me change the vimeo videos that are in tose boxes to youtube ones?

Thanks for your help

Tracy