if u download mannasim folder.. inside the mannasim/ folder (there will be a ns-modified-folder/ that contains set of files to be pasted to different location)
Copy the files from the ns-modified-files/ to these locations
ns-allinone-2.35/ns-2.35/apps/udp.cc
ns-allinone-2.35/ns-2.35/common/ns-process.h
ns-allinone-2.35/ns-2.35/common/packet.cc
ns-allinone-2.35/ns-2.35/common/packet.h
ns-allinone-2.35/ns-2.35/Makefile.in
ns-allinone-2.35/ns-2.35/tcl/lib/ns-default.tcl
ns-allinone-2.35/ns-2.35/tcl/lib/ns-lib.tcl
Once everything is done, go to the terminal and type the commands one by one