DECLARE @M TABLE
(
    ParameterName NVARCHAR(20),
    ParameterValue NVARCHAR(MAX)
);
INSERT INTO @M
VALUES
('1', 'Napis1 &<'),
('1', 'Napis2 &'),
('1', 'Napis3'),
('2', 'aaa'),
('2', 'bbb'),
('3', 'a');

SELECT * FROM @M

SELECT DISTINCT
    ParameterName,
    RemappedValues = STUFF(
                              (
                                  SELECT ';' + ParameterValue
                                  FROM @M AS M2
                                  WHERE M2.ParameterName = M1.ParameterName
                                  FOR XML PATH(''), ROOT('ParameterString'), TYPE
                              ).value('/ParameterString[1]', 'nvarchar(max)'),
                              1,
                              1,
                              ''
                          )
FROM @M AS M1;