Can I cancel purchase from the store ? What Is the process ? I bought it a few hours ago and have deleted it.

All purchases are considered final, but you can try the 'report a problem' link to contact iTunes Support and see if they will refund or credit you : http://reportaproblem.apple.com

If the 'report a problem' link doesn't work then you can try contacting iTunes Support via this page : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption

Just a note for your edification... Deleting the purchase doesn't do a thing other than to remove it from your device. As the terms of all of the Apple iTunes/App Store and iBooks Stores are "All sales final", you will have to contact a human being via email or via the links that King Penguin provided. It will be up to their discretion as to whether they decide to refund the purchase price to you.