youtube embed

I am new to wordpress.. I am working on this site https://www.storiesfromnepal.com .. On the front page i have showed a video from youtube by pasting the youtube embed code changing the width and height of the video .. My problem is when i click on the read more and view the video i want it to be of a different size how can i do that ..

For example: I want the video here

https://www.storiesfromnepal.com/?p=113
to be of a different size

Please help .. I want to complete this theme ..

Yogesh