How do you access preferences for changing size of the launcher bar or icon size, etc?
Make sure you have the CompizConfig Settings Manager, which manages the settings for the plugins of the window manager including the Unity UI, installed:
sudo apt-get install compizconfig-settings-manager
Then run it from Preferences and find the Unity plugin, Choose ‘Experimental' tab.
Adjust the value of ‘Launcher Icon Size' by simple scrolling. The default value of ‘Launcher Icon Size' is 48, try to set the value around 40