Manual:Chmod

The   command (abbreviated from change mode) is a Unix command that lets a programmer tell the system how much (or little) access it should permit to a mediawiki file.

Accessing files
If you are using FTP software, there is usually a menu option or button that says "Change Permissions," click this option. You have choices of R(read), W(write), and X(execute).

If you are using a program such as PuTTy, you need to use the "chmod" command.

Recursion
If you want to make everything under the ./www subfolder be 755: