this should be in the wiki
before connecting to the site on the site list of winscp make sure the protocol used to connect to the node is SCP
If it is not scp click on edit and change it.
Then click on advance
and choose scp/shell on the left pan. and in the shell menu select sudo su -
click OK
save the configuration and reconnect. you will be able to edit every file on the node with winscp