We strongly recommend that you make a copy of the out-of-the-box report before you modify it.
After copying the report to your own report folder, edit the report from Jaspersoft Studio.
We also recommend that you publish the report to the reporting server to test your changes instead of previewing it from Jaspersoft Studio.
Please refer to the following documentation regarding JasperSoft Report Studio
Getting Started with Jaspersoft Studio | Jaspersoft Community
There is a section regarding Editing reports.