first you must to change the root pasword, use in x terminal sudo gainroot passwd user and set a new password for root, diferent that you use to login in winscp (went you type the pasword can not see the letters you write) retype the password and you get it changed, after that in winscp in the part of loggin write root and in password your new password for root. and that is all. i did it whit putty, but i think so is same from xterminal, just try it