We cannot edit the underlying theme files here at wordpress.COM because this is a multi-user platform which means we all share the same underlying theme and wordpress files. Any change by one person would change it for everyone using that theme.
If you have CSS editing experience, wordpress does have the paid custom CSS upgrade, which will allow you to stylize the theme, but it does not allow you to change the functionality. Also, there is no official support for the CSS upgrade, and few here in the forums with much CSS experience, so you should figure that you are on your own.
Also note that most of the themes here have the same design for all the pages which means if you hide elements from one page, it hides them from all pages.
The widgets in the sidebar can be removed without the CSS upgrade by putting a single blank text widget into the sidebar. The other default widgets will then disappear.