Problem with the case of letters when using User defined function

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SQL-Server

Hello!!

I have created a user defined function(Scaler function) in sql server 2008. It returns me an integer value based on the query. The problem that i am facing is that it is reading Both "Admin" & "admin" as same value and then returning me the wrong output. Here is the function

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER FUNCTION [dbo].[UFNLogin] 
(
	@UserName varchar(30),@UPassword nvarchar(max)
)
RETURNS int 
AS
BEGIN
declare @Exists as int 
	if (Select count(ID)from Users where UserName=@UserName and UPassword=@UPassword)>1
set @Exists =1
else
Set @Exists=0	
return	@Exists
END

For example that if i enter user name "Jack" and Password "Admin" which is in the database, then it is returning 1 output but if i enter "Jack" ,"admin" then also it is returning me 1 as output whereas admin is not in the database.