you have to join tables based on common columns, it is basics of sql.
Update can also have join like:
update UD
set FirstName = @FirstName,
MiddleName = @MiddleName,
LastName = @LastName,
Mobile = @MobileNo,
Phone = @PhoneNo,
PeviousName = @PreviousName,
FathersName = @FathersName,
DateOfBirth = @DOB,
Gender = @Gender
FROM UserDetail UD
INNER JOIN LOGIN L--OR whatever your table name is
ON L.UserDetailID =UD.UserDetail
WHERE UD.LoginID = @LoginID
refer Join Fundamentals for learning join