Open the Terminal and try to install such one by one 1) sudo add-apt-repository ppa:tualatrix/next 2) sudo apt-get update 3) sudo apt-get install ubuntu-tweak then go to website www.gnome-look.org for gtk3.0 themes and icons Now Follow the steps 1) Open home folder and press Ctlr+h 2)Create a folder name as .themes and .icons and extract the theme downloaded file to .themes folder and Icons downloaded file in .icons 3)Now open Ubuntu Tweak from Dash board and go to Tab Tweaks and then choose Themes and there with in select GTK theme and find your downloaded theme there and you can change Window theme by same as you done in GTK theme. And see the video in YouTube and change according to it https://www.youtube.com/watch?v=inZ9uYYILXU
It is most Important to remain updated with new technologies in our daily life.