If you are on *Nix system, login to shell and then

man patch

This would give you all the necessary details of how to apply patch to a file.
Create a backup of original file before applying the patch.

Lenghty way around is vi filemane
Then do the necessary changes

-- means that the said line would have to be removed from existing file
++ means that the said line has to be added to existing file.

HyTC