Because of the complexities of each page type r is not possible to change one page type to another page type. You need to My Websites -> Main -> Pages -> Create New Web Page selecting the page type you want to use, then edit your new page to contain the content you want to display.
You can copy and paste the text content from one page to another. If you wish to retain the formatting in the text editor click the "source" atop the editor first, then copy, then hit the source tab atop your new page before your paste the content. This will retain the formatting, links, and any images in the text area.