There are two simple ways you can delete a file in your File Manager.
OPTION 1 - select a file by clicking the checkbox next to it. Then RIGHT click on the filename or row and select "Delete".
OPTION 2 - select a file by clicking the checkbox next to it (or click on the filename). Then HOVER over the row and a DROP DOWN ARROW will appear.
Then click the drop down box and various options will show up. Click the DELETE option.
A confirmation box will appear asking you to confirm that you really want to delete the file.