In case you are not using cpanel but a normal FTP program, there is usually a built-in function for this. In FlashFXP for instance, you can right click a file on the server and choose chmod. Then choose your permissions, instead of what Corey says I think 644 will not be enough. Since it's only during installation you can always set it to 777, but do not forget to change it back after installation for security reasons.