Hide Default reports

Hide Default reports

Hi. 

I'm trying to hide the default reports so the team can see only the custom reports we made.
How can I acomplish that?. 
I know how to create a folder and assign permissions to it, but I can't (or don't know how to) do anything with the existing default reports. 
Also I would like to know how to change the permissions of an existing folder.
Thank you.