Once you are logged in, you can edit the content of this page by clicking “Edit Page” at the top of the screen from the front end, or by clicking “Pages — About” in the back end (WordPress dashboard).
When you have the page/post editor open, you can use the icons to format text, insert images (“Add Media”) and embed things like video and audio using shortcodes (“H” icon in the editor).
To put a picture at the top of the page above the text, insert a Featured Image to the right of the text editor.
See our detailed help section for more ways to edit Posts and Pages.
The page editor is quite intuitive, but if you are stuck then you can Google “WordPress page editing”. There are lots of resources on the web, including tutorial videos and written guides.