To get started with changing the name of a Variance Report Metric you will want to navigate to the specific metric from the "Data" section as shown below:
From here, you will want to click "Variance Report" as shown above. From the Variance Report section you will see the variance data you are currently tracking and a "Setup" icon in the top right corner.
Click "Setup", you will see a list of the metrics you are tracking. Hover over the specific variance metric name you would like to change and click the edit icon. From here, you will be able to change the metric name on the left side as shown below: