Same as moving, deleting, or renaming, you can change the permission for a file/directory via the File Manager. To do that select the files/directories for which you would like to change the permissions. After that click on the Permissions button and set the permissions you would like.
If you accidentally set wrong permissions for a file/directory and you are not able to change them back you can contact our technical support by opening a trouble ticket from the Hosting Control Panel > Support > Trouble Tickets.