how to use diff files?

[root@next1]

This may be a silly question, but how do diff files work?  specifically,
I want to upgrade g++ from 1.37.0 to 1.37.1.  I ftp'ed the diff file, but
can't seem to get it to work.  I tried ( cat fname.diff ; echo w) | ed
but that doesn't go.  I would appreciate the responses, and will send a
summary to be included in the next Freq. Asked Q's.

-- 
Dave Strout
dastrout at miavx1.acs.muohio.edu
dastrout%miavx1.bitnet at pucc.princeton.edu
root at next1.acs.muohio.edu
513-523-8245