How to print from iPad to HP4500 wireless?

That printer is not on the list of approved Airprint printers.

http://support.apple.com/kb/ht4356

You will have to use a universal printing app, such as Print Central or Print n Share. Look in the app store for printing options.

I am using FingerPrint from collobos.com for my non-AirPrint HP and Canon printers.