ファイルの削除ができない

The Trash Can within a project is for deleting whole pages from a project, and will be inactive if there is only one page in your project. 

To delete elements from your project e.g. images, shapes, text etc. click on the element and use the Delete key on your keyboard. With text it is often easier to click the layer to select the text box, so that you are not accidentally in text edit mode and deleteing only one letter - it happens to me all the time!