How do I change default size settings for images inserted in posts?

DW Focus overrides core wordpress settings and changes “medium” size for inserted images in posts from 400×225 to 230×130. This is ridiculously small. I want to stop the theme from doing that so it uses 400×225 as the default size for medium thumbnails. How do I change this?
 
Also, on this site can you PLEASE disable that really annoying Halloween plugin? It floats over everything, obscuring text and buttons, and if you accidentally click on it, it opens a new tab. It’s very, very irritating and bad practice. Disable it!