FileZilla is a popular free FTP client which is used to upload, download and manage website files/folders. Its functionality extends to setting permissions on files and folders, and using the steps below you may seek to adjust those:
Browse to the location where the file/folder is you wish to adjust the permissions on.
Right click the files/folders you wish to update.
Select File Permissions from the drop down menu.
Select the appropriate boxes or type in the Numeric Value of your new permission set.
Click Ok.
Adjusting permissions may be completed using most FTP clients; if you are using an alternate client, please refer to their help documentation for instruction.