Be careful: not all clients support the newest algorithms. Example: Ubuntu 12.04 ssh client doesn't support curve25519-sha256@libssh.org (I'm still googling how to upgrade to the latest openssh, anybody has the answer?)
In general, check that you are still able to connect to your server before closing your last ssh connection to it.
That parameter is only for SSHv1 and if you have SSHv1 enabled you've already lost.
What they are refering to is the Key Exchange method named "diffie-hellman-group1-sha1" which uses a 1024-bit DH group. You can disable this with use of the KexAlgorithms parameter. Starting with OpenSSH 6.6 it is already disabled on the server side, but still allowed with the client. There are severe interoperability problems with embedded devices if disabled.
Be careful: not all clients support the newest algorithms. Example: Ubuntu 12.04 ssh client doesn't support curve25519-sha256@libssh.org (I'm still googling how to upgrade to the latest openssh, anybody has the answer?)
In general, check that you are still able to connect to your server before closing your last ssh connection to it.