Valuation of closing stock

Dear all,

There is a little bit confusion in my mind regarding closing stock value which I want to discuss with u to clear it.

lets take example:
I am dealer of Authorized computer seller &I have purchased 4 computer @ Rs 50000/- each Value becomes Rs 2 lac. as my closing stock value.

After few days due to some reason I insist my supplier to give these computers @ Rs48000/- each and they agreed for that.

Now I issued a debit note of Rate difference of Rs 2000/- for 4 computers Value 8000/-.
After issuing debit note in my Tally software I have seen that My supplier has been debited to Rs 8000/-. But my closing stock value still shown that Rs 200000/-.

so I just want to know How it will get reduced.....?

kindly give me suggestion.