How to change WordPress User Role capabilities

WordPress blog User with role “Author” can upload images to the blog server, but he can not use it in his/her posts. Any HTML tags are immediately hidden from post text after “Author” saves his draft or post. The same user with role “Editor” stores post with all HTML tags he includes in it with success. The problem is that WordPress automatically applies HTML filters to all author’s content if he has not “unfiltered_html” capability in his role.