Scroll down to the bottom of the Report Editor page and click the Metric ID of the Project Metric you want to edit.
Make your changes and click Update.
The changes you can make include:
Changing the Metric ID
Selecting another existing report column to map the Metric Value and Target Value columns to.
Selecting another existing report column OR create a new report column to map the Indicator Icon; Indicator Status; Formatted Metric Value; Formatted Target Value; Formatted Warning Value; and Formatted Danger Value columns to.