Sorry - my installation of Project 2013 has no report named "Upcoming tasks" - so I'm still guessing it is a custom report.
Is it a table based report? If so, click in the table and on the field list on the right - there should still be an option for filters. To create a report - open the existing report, on the Report Tools - Design tab - select "Manage" to rename the report or Copy to create a copy of the report and edit.
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