how to modify a library

i having difficult time getting arduino make ethernet connection (i.e., hangs on "ethernet.begin(mac)") , want implement change dhcp.cpp library file recommended else on forum; however, didn't how go modifying library file, rather told me line insert where.

tried google issue of how modify library file using arduino ide, , found -- http://forum.arduino.cc/index.php/topic,37294.0.html.  but it's not working me, i.e., copy .cpp , .h lib. files sketchbook directory , restart ide.  then can find .cpp file within ide using file/open menu (i.e., file not in sketchbook), , when try open message: "processing can own sketches , other files ending in .ino or .pde".

once above problem solved, i'm still not sure how compile revised library file , ensure 1 gets loaded.

any suggestions on how appreciated -- can tell, it's first project!!

find source file want change. standard libraries shipped ide, under libraries folder in arduino software installation directory. libraries have installed separately, these should have been installed in libraries folder within directory sketches stored.

open file want change in favorite text editor. if don't have favorite use default notepad editor. save changes. when compile sketch in arduino ide, use whatever version of library has been saved disk @ time.

before changing library source file, suggest save copy of original file somewhere else can revert if necessary.

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