Just to add to what's below.
If there are no screws at the bottom they could well be spring clips. Have a look at this PDF (give it time to load) and look at the instructions on the very first page.
http://www.arcsystems.biz/manuals/%20SPL3002.PDF
Dont be suprised when the PDF opens vertically just scroll down to the bottom!
GB in Wales
March 2013