There are two parts of a scheduled report that can be updated:
Report Name: this would update your report parameters (i.e. date range, sales reps, options, etc)
Edit: would update the recurrence, if the scheduled report is still active and email content

Part #1 - How to Edit a Scheduled Report's Parameters:
Click on Reports
Click on the Scheduled Reports tab
Click on the Report Name that you would like to edit
Make the changes needed
Click on the dropdown arrow next to Run Report
Click on Schedule This Report
Part #2 - How to Edit a Scheduled Report's Parameters:
Click on Reports
Click on the Scheduled Reports tab
Click on the Report Name that you would like to edit
Make the changes needed
Click on the dropdown arrow next to Run Report
Click on Schedule This Report
