If you need to reset an uploaded file or clear it altogether, the show upload can be tweaked into

show upload "Please upload File 1" editable:"upload1" with Hash, Name

The hash should be a 32-character hexadecimal hash, such as the one obtained from Files.Hash, and the name should be a valid filename (no forbidden characters), more importantly it should have the proper extension in order to be able to read the file .

If both the hash and the name are "", then that particular line is ignored (meaning, show upload "MyFile" with "", "" will clear the tile).