You do not have to do anything, if the server is changing its preferences. WinSCP and the server will automatically agree on the best mutually supported algorithms.

Thank you for the reply. i just wasn't sure it would use the 256,and didn't want a kick back, when we connect. because the site I'm connecting to, is changing to only except that encryption on the 30th.
thanks.

The dh-gex-sha1 stands for Diffie-Hellman Group exchange:
https://winscp.net/eng/docs/rawsettings#kex
It includes both SHA-256 and SHA-1 (in that order of preference).

when using the advanced key exchange selection,and picking diffie-hellman group exchange. then generating the seccion URL/code for powershell schript. it is putting KEX=dh-gex-sha1

How do I know that that is diffie-hellman-group-exchange-sha256?
shouldn't it be dh-gex-sha2 or dh-gex-sha256.
I need to make sure the key exchange I am using is:
===ssh-kex
diffie-hellman-group-exchange-sha256
diffie-hellman-group14-sha256
I've searched every where on WinSCP site, and see no formal statement of what setting to use inn the command KEX=.
thanks for any help with this.
Lynn...