i can't link the slider to their posts?

there is a settings in the theme that allow me to link the posts in the slider to their posts, but when i try it the homepage doesn’t open, it goes white, i don’t know why

and when i disabled it i found out that pictures i put in the slider are not in the right size, they are smaller i don’t know why either

can anyone tell me how to fix that or which are the right files to try to edit them in?

thanks alot