For that, move the mouse pointer on top the report name in the report server folder and you will get a down arrow. Click on it and then select Manage. In the Manage page put a tick at the Hide in tile view and click on Apply button.
Then go to the report server folder and you will not see that report anymore. But still you can drill down to that report from another report.
If you want to show that report in the Details view again, click on Details View to get the detail view of those reports and all the report are visible there. Then follow the steps as you did earlier and get the Manage page. In that remove the tick at Hide in tile view property.