To be able to pull reports for a larger period of time you need to change the events database retention period setting. Follow these steps:
Note 1: Because you are increasing the number of days to keep a history of events, keep an eye on how much free space gets left on C:\ as time goes by; yet that the events database will grow larger in size.
Note 2: Keep in mind that after the retention period of events gets increased, you will not be able to pull a report for that amount of time until the number of days set have elapsed since the date it was set. Because events that fall off that retention period get purged every night with the nightly jobs, increasing the retention period will not make old events appear, they had been removed already.
Note 3: Previewing a report could show incomplete information for the selected Date Range. To get the complete report, press the button to download the document on the selected file format.