Yes, access to your server using Putty and as root execute the commands. If you are login as a normal user, you can use sudo to execute the commands or to login as root and then execute the commands.
As a normal user with sudo privileges:
sudo chown -R hestiamail:hestiamail /etc/roundcube/
sudo find /etc/roundcube/ -type f -iname "*php" -exec chmod 640 {} \;
Or as a normal using sudo to switch to root user:
sudo su -
chown -R hestiamail:hestiamail /etc/roundcube/
find /etc/roundcube/ -type f -iname "*php" -exec chmod 640 {} \;