Don’t be scared if you’re not comfortable with terminal commands. Just copy the code via Ctrl+C, then paste into terminal via Ctrl+Shift+V and finally hit Enter to run.
To get started, press Ctrl+Alt+T to open a terminal window. When it opens, run below command to reset Unity and Compiz settings:
dconf reset -f /org/compiz/
After running previous command, you need to run blow command to restart Unity.
To get back the default set of Unity Launcher icons, run below command and then log out and back in.
If you want to restore default icon theme, use Unity Tweak Tool which is available in Ubuntu Software Center.