The Advanced Reporting System allows you to do powerful customizations to your Reports. The reporting here does require knowledge of the Liquid Templating Language but can give you tremendous control over your reports. For an overview of Liquid basics, please visit http://docs.shopify.com/themes/liquid-documentation/basics.
Accessing the Advanced Editor
From the profile drop down in the top right corner, click Admin. Then select Reports from the left hand navigation.
Once you are on the Reports page, locate the report you want to edit and click Edit. You can only access the Advanced Editor from a report that was previously created. If it is not in the reports list, you will need to use Create Report and create a report to be edited.
From the Report Editor select Advanced Editor.
The Advanced Editor is setup using the Liquid Templating Language and can do customization beyond what the basic editor can do. This gives you tremendous control over the look and feel of your report. Some things that you might do are introduce constants for averages, add a logo or other design to your report, or create complex operations.
Note: If you make a change using the Advanced Editor, you will be unable to access the basic editor for that report.