Depending on how you have your DIP switch set up -
1) Del is the key marked Delete (button where \| is on a standard US keyboard), and BS is Fn + that key.
2) Backspace is the key marked Delete, and delete if Fn + ~`
I'm not explicitly familiar with the Lite extension mode, but I assume that it's the second configuration of the above two.
EDIT: From the diagram on the other page, Lite extension is the mode I use on mine... So del if Fn + `~