By default each report has a date range it will run for every time it is loaded.
Click the cogwheel to edit the date range on the fly. once you've changed it, it can be reset to the original date range anytime.
The report 'date range' button will show the new temporary range:
Please note that this new range is only temporarily applied and will only affect what you can see - anyone else with access to this report will continue to see the default range.