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:
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!