You can not update past metrics and please be aware that Retail Express may not have all of the metrics available.
You can delete the whole metric though.
To delete all events for a given metric and remove it completely from your account, navigate to the Analytics > Metrics. Here, you will see a list of your account metrics. Any metric that has a trash can icon beside it on the far right can be deleted. Click the trash icon and then click Delete Metric to remove the metric along with all associated event data from your account.
