hot to delete a file in kindle /usr/share/blanket/screensaver/

I try to delete a file at
/usr/share/blanket/screensaver/
but got error message : readonly file system, checked permisson of the files and folder , it is 755, no permission to write or delete

tried su command, does not work,
is that possible to delete kindle system file at /usr/share/blanket/screensaver/

anyone give me a hint, thanks!
just want to a blank screensaver
:thanks: