I have been trying to install Opencv following the instructions given in this link [https://github.com/manashmndl/FabLabRpiWorkshop2017/wiki/Painless-OpenCV-in-Raspbian-Stretch]
I need to copy files from /home/pi/CompiledOpenCV/usr/local to /usr/local
but have no permission to do so.
How can I change permission of the folders or copy files using command line.
You should never change permissions on system directories like /usr/local. For copying you can use the sudo command and maybe you have to make the copied files executable with chmod and/or add the user to a proper group with sudo adduser $USER $GROUP. And I think your executable should be copied to /usr/local/bin. But in general I don't understand why do you take so much effort to compile OpenCV from source and install all by hand. You can simply install the libraries from default repositories with e.g.:
rpi ~$ sudo apt install libopencv-video2.4v5
or what else library you need. Look with
rpi ~$ apt list *opencv*
