Did you mean free storage space? Deleting files from the root directory is useless, the user partition (visible drive) is at a fixed size. However, if you must know, the directory is in /usr/share/blanket/screensaver/
However, deleting it has no effect, except from you having no screensavers
Also, if you want to change the screensavers, I do not recommend directly putting pictures there, but using the screensaver hack (linkss), which symlinks the images so that overflowing the root directory will not result in a bricked kindle
Edit:
If you actually meant ram, you are probably running a large ram-eating program.
If you want to know, you can stop the screensaver using helper+ in kual.
Executing "stop lab126_gui" in a shell will halt the user interface, freeing ram.
Also, you can create a swap file described
here to gain more ram from the flash drive