You use the cast command to
set your range-weapon to the
spell you want.  Example:
'cast burning hands

sets your RANGE weapon to
'spell: burning hands'

If you don't know the spell,
shows which spells you do 
know.

It is helpful to bind strings
like 'cast burning hands'
to keys.  see 'help bind'

'help range 
for more information on
range weapons.