Thank you Martin for the information.

If you are interactively using WinSCP GUI, you do not need to do anything regarding the host key. The first time you login after the change, you will be prompted, if you trust the new host key:
https://winscp.net/eng/docs/message_security_breach
Verify the fingerprint on the prompt against the one the administrators have provided (hopefully they did).

Regarding the ciphers. We do not not support old versions of WinSCP. But I believe that 5.10.1 does support at least the aes256-ctr. But you should upgrade anyway. 5.10.1 is four years old and it's a beta version!

I am using Winscp version 5.10.1 to connect to a server using SFTP protocol. As a security improvement, SFTP Host key of the server is going to updated from 1024 bit DSA Host Key to 2048 bit RSA host key with below cipher option.
aes256-ctr
twofish256-ctr
twofish-ctr
aes128-ctr
twofish128-ctr
cast128-ctr

Do i have to update this new SFTP key manually? Is there any option where i can check this?
If I have to update SFTP key manually, how to do that in prior?

Also does my existing Winscp version support this new encryption configuration or I have to update winscp version?

Thanks in advance.