I figured out how to mass delete the reports. Here are the steps I took:
1) Log into my ArcGIS Business Analyses
2) Open the project in which the reports your want to delete are located
3) Click on "View Full Table" in bottom left corner
4) Under "Previously run reports", right mouse-click on the "PDF Report" symbol at the far left of the1st report to be deleted to select/highlight that report (clicking anywhere else in the row will open the report which is not what you want).
5) Use the "Ctrl" key + right mouse-click on the "PDF Report" symbol to select/highlight additional reports to be deleted (If a report is selected in error, simply Ctrl+click to unselect)
6) Right click on the "..." at the far right of any highlighted row
7) Right click on "Delete items" and select "OK" to confirm