See Here > Download Past Purchases
now want to change the laptop. can all the apps can be transfered to new laptop
From your OLD computer...
Copy your ENTIRE iTunes FOLDER to an External Drive... and then from the External Drive to your New Computer..
Full Details Here > http://support.apple.com/kb/HT1751
Yes its possible!
If you want to do this, You should install the iTunes on the new computer, and then log in with that Apple ID You used to pruchased these stuffs. Don't forget to Authorise the new computer to use Your Apple ID (Store / Authorize this computer). Now go to the iTunes Store at the main screen u can find at the Quick links / Pruchased. There You can see the list of the applications and there You should find a download all button.