The ciphers for ssh are configured in the
/etc/ssh/sshd_config file so you will need to disable the deprecated ciphers by modifying lines in the sshd_config file.
First off make a backup of the existing config file.
To create and start using SSH keys you will need to login to your server using putty or what ever tool you have.
To create the SSH key you will need to run
ssh-keygen -t rsa -b 4096
You are then prompted with a few options you will be asked for the directory to save the key file to, default is...