Remove Duplicate Character from String

CREATE FUNCTION[dbo].[FUN_Remove_Duplicate_Char](@Input[varchar](max))
RETURNS[varchar](max)
AS
BEGIN
DECLARE @Count int;
DECLARE @Return_String[varchar](max);
DECLARE @Char_Index int;
DECLARE @Temp_Str[varchar](max);
SET @Count = 0;
SET @Return_String = @Input;
WHILE @Count <= 255
BEGIN
SET @Char_Index = CHARINDEX(CHAR(@Count), @Return_String, 0);
IF(@Char_Index > 0)
BEGIN
SET @Temp_Str = SUBSTRING(@Return_String, @Char_Index + 1, LEN(@Return_String));
SET @Temp_Str = REPLACE(@Temp_Str, CHAR(@Count), '');
SET @Return_String = SUBSTRING(@Return_String, 1, @Char_Index) + @Temp_Str;
END
SET @Count = @Count + 1;
END
RETURN @Return_String;
END

SELECT dbo.FUN_Remove_Duplicate_Char('Hello How Are You') AS String_;