How do I print from my ipad to Epsom stylus sx515w ?

It's not on listed this page as supporting AirPrint : http://support.apple.com/kb/HT4356

So you will need an app. Epson have their own iPrint app in the store, you could see if that works with it. If it doesn't then there are a number of third-party printer apps which might do so e.g. Print n Share, PrintCentral Pro etc

Google search for "AirPrint server" and include Mac or Windows for your personal computer operating system, and you will find several options.