Install PixAnalytic extension ( see Installing and uninstalling ).
Go to Extensions> Plugin Manager. Find the System - PixAnalytic and click on plugin to open it.
Select enable the plugin.
Choose the type of analytics you are using, Classic or Universal. Enable that tab add your Google Analytics code to that tab.
If you are transitioning from Classic to Universal Analytics you can enable both types and add the different ids to each type.
Save the changes. You have now installed PixAnalytics on your site!