medium image post type

hello i just set up the theme and made my website, but i have a porblem with the post types, at this page i can not make it to blog image medium size, it is not working,. i dont want to set the them up because i hae changed the style sheet.

would you please send me the working files that only make the page to medium size.

thnaks in advance.

and i tried this answer, it dows not work for me for the changing it to a category page

i made it! :slight_smile: your answers are really helpful! thank you very much for olders…
i choosed a page for blog post, when i cancelled it, it changed to medium format.
i have 2 more questions, how can i change the blog image dimensions? its 230x230 now?
and how can i delete line between the content area and footer? its like

thanksi in advance,

and one more, if i want to use sidebar, how can i enable it? i add some widgets for rightsidebar, but i can not enable it for a category page

thank you!