It looks like you already have it installed.
If you want to remove something you installed just run
sudo apt-get remove libopencv-dev
then you can install a new version
sudo apt-get install libopencv-dev
It is also pretty easy to compile from source and then you always know where it is located and you can manage versions and build parameters.
If you want to compile opencv it is pretty easy
sudo apt-get -y install libopencv-dev build-essential cmake git libgtk2.0-dev pkg-config python-dev python-numpy libdc1394-22 libdc1394-22-dev libjpeg-dev libpng12-dev libtiff4-dev libjasper-dev libavcodec-dev libavformat-dev libswscale-dev libxine-dev libgstreamer0.10-dev libgstreamer-plugins-base0.10-dev libv4l-dev libtbb-dev libqt4-dev libfaac-dev libmp3lame-dev libopencore-amrnb-dev libopencore-amrwb-dev libtheora-dev libvorbis-dev libxvidcore-dev x264 v4l-utils unzip
then get opencv 3 which is the latest version
mkdir opencv
cd opencv
wget https://github.com/Itseez/opencv/archive/3.0.0.zip
unzip opencv-3.0.0.zip
then compile
cd opencv-3.0.0
mkdir build
cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D WITH_TBB=ON -D WITH_V4L=ON -D WITH_QT=ON -D WITH_OPENGL=ON ..
make -j $(nproc)
sudo make install
You can also use ccmake .. if you want to configure the options a slightly easier way. Then at that point just point your include path to your build directory, or your make install directory which should be /opt/opencv I believe.