Who ever is going to change the security setting of a file has to have an admin right. If he does then all he has to do is right click on the file that is desired to be modified and click on property then security settings and click on add-> then on the window that opens up click on the user name and click ok or click on check name button select the user name and click okay once the user name added to group highlighted then one can modify the permission settings from the permission box. cheers!