Please see the following links before reading on to ensure you understand the commands:
http://codex.wordpress.org/Hardening_WordPress
http://codex.wordpress.org/Changing_File_Permissions
You can run these commands from the root of your website via SSH to change the file permissions to the Wordpress recommended ones:
find . -type f -exec chmod 644 {} +
find . -type d -exec chmod 755 {} +