This is usually the case if the model does not directly show what series it is part of. I checked ACER website and found that 5315 seem to belong to the 5310/5710 series. Try this URL:
http://www.frc-tech.com/docs/manuals..._5210_BOOK.pdf
You can download the 28MB plus PDF file for a 5710/5310 series. Just make sure the locations for your laptop matches the ones in the manual.