The original iPad cannot be updated past iOS 5.1.1. If the app you want to use requires a later version of the iOS you will need to update the iPad. Apple does not have a trade in program. But there are many ways to sell your iPad should you want to replace it.
Presently the Apple Store sells a 16 GB iPad with retina Display (iPad 4) that is Wi-Fi only for $399. There are several other more robust models at higher prices.
Apple does not do electronics trade-ins.
You can try to sell your iPad on eBay or local media websites.
A web site like gazelle.com will give you some cash for your iPad, but it wiil not be enough to purchase a new iPad.
You can check Apple's website for certified refurbished iPads that will be a c heaper than new.
OR, if you have authorized Apple resellers in your area or authorized resellers online, you can opt to purchase a used, newer iPad that may be much cheaper than Apple's prices.