How do I upgrade my ipad 1st generation ios from iOS 5.1.1 to iOS 6.0 so that I can use more apps from the app store?
Besides that you can't do that, you really don't want to do that. The reason is the original iPad only has 256MB of DDR RAM. It's pretty amazing that Apple squeezed out so much wonderful functionality out of that puny amount of RAM (by today's standards). Subsequent versions of iPads doubled and quadrupled the amount of RAM, and subsequent versions of iOS has added many new and exciting features that would, if capable of running on the original iPad, cause it to slow it to a crawl and cause many "out of memory" crashes and reboots.