i have deposited the required form in bsnl office at morninig 30th june 2009 for plan change from 299 c to 500c .
the people in bsnl office told me that the plan change will be effective from 1st july . but when i saw in my portal the plan 299c is existing .
what to do to get 500c immediately.

Well.. logically should change by 1st July ie. today but I guess it will not as they are not very quick to make changes, you should have deposited it atleast 4-5 days back. Anyways, wait for tonight and on 2nd July meet them.

I had once applied on first of that month.

Hmm, it takes just about 2 day and 3 days at most in case of another day being a holiday / sunday!
You can get to know this by calling 1500 from your BSNL Phone. It is a toll free customer Care number! They provide complete information!