Reg:sql server two users manuplating data at a time

Use transaction in your code.See below:

--For Update 
--Executed by USER1
BEGIN TRANSACTION
BEGIN TRY
	UPDATE [Employee] SET Salary=Salary *.5 WHERE Salary>1000
	COMMIT
END TRY
BEGIN CATCH
	ROLLBACK
		SELECT
			ERROR_NUMBER() AS ErrorNumber,
			ERROR_SEVERITY() AS ErrorSeverity,
			ERROR_STATE() AS ErrorState,
			ERROR_PROCEDURE() AS ErrorProcedure,
			ERROR_LINE() AS ErrorLine,
			ERROR_MESSAGE() AS ErrorMessage
	
END CATCH

--For Delete
--Executed by USER2
BEGIN TRANSACTION
BEGIN TRY
	DELETE FROM [Employee] WHERE Salary>1000
	COMMIT
END TRY
BEGIN CATCH
	ROLLBACK
		SELECT
			ERROR_NUMBER() AS ErrorNumber,
			ERROR_SEVERITY() AS ErrorSeverity,
			ERROR_STATE() AS ErrorState,
			ERROR_PROCEDURE() AS ErrorProcedure,
			ERROR_LINE() AS ErrorLine,
			ERROR_MESSAGE() AS ErrorMessage
	
END CATCH

In that case when USER1 runs UPDATE command it will put an EXCLUSIVE LOCK to the Employee table so the DELETE command of USER2 will wait until the USER1's UPDATE command to be finished.