I have used my dad's apple id to download the apps. But now i am using my own account and its not letting me to update the old apps. Help me guys.

You need to use the Apple ID that made the Original Purchase to Update...

Anything Downloaded with a Particular Apple ID is tied to that Apple ID and Cannot be Merged or Transferred to a Different Apple ID

Apple ID FAQs > http://support.apple.com/kb/HT5622

OR... Delete those Apps and Download them using Your Apple ID.

Correct. All purchases are tied permanently to the Apple ID with which they were purchased. Either you have to use your father's Apple ID to update the apps or repurchase them using your Apple ID.

So that you don't misunderstand AnaMusic's last sentence: you cannot simply download them again unless they were free apps. You must repurchase them using your Apple ID.

That likely means you are logged into iTunes with your old Apple ID. Sign out, then sign in and use your new Apple ID and password. Then try again.

Also, be sure you have reconfigured your iPad with your new Apple ID.