Twenty Theme resizing image

I recently updated the Twenty Ten Theme and now my images are being auto resized in my articles.

Full size is 800px x 600 px, but they are being resized to 768 x 561.

Would really appreciate any help with this thanks.

I am using twenty ten child theme for https://www.eatandtravelwithus.com/2016/08/ultimate-seoul-travel-guide/