If all your uploaded files have permissions set to 600, you will need to alter the vsftpd config file.
sudo nano /etc/vsftpd.conf
Look for the line
#local_umask=022 (You can search in nano with
Uncomment this line by deleting the # sign so it looks like this
Save file and exit. (Press
Y and then press
sudo service vsftpd restart
Upload a test file via FTP and the permissions should now be set correctly.