https://workonlinux.wordpress.com/2016/02/09/how-to-configure-the-ssh-service-to-use-a-unique-diffie-hellman-moduli-of-2048-bits-or-greater/#comment-1282
Step 1:
Take a copy of /etc/ssh/moduli and /etc/ssh/sshd_config file first
Delete lines from /etc/ssh/moduli where the 5th column is less than 2000.
awk '$5 > 2000' /etc/ssh/moduli > “/usr/src/moduli”
mv “/usr/src/moduli” /etc/ssh/moduli
Step2:
Add the following ‘KexAlgorithms’ in /etc/ssh/sshd_config
KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256
Step 3:
Restar SSH service on the server
/etc/init.d/sshd restart