copy and replace only files with new content

copy and replace only files with new content

i have about 16GB of data which takes about 6Hrs to copy
However about 100mb of the data has changed and i wish the script just
scan and look for a new file either by size or date and then replace and
copy if a file is absent
Kindly help
NOTE please click the link to get a copy of the scripts i currently use
http://netit.com.ng/do_rep.sh http://netit.com.ng/do_copy.sh