Please help update to version 5.1.1 for my ipad1

you should just need to plug your iPad into a computer with iTunes installed. It will automatically prompt you to backup and update the device to the latest available software.

A first generation iPad cannot be upgraded beyond iOS 5.1.1. That is the most up to date version of iOS possible for that device. As mentioned, plug it into iTunes and select update from iTunes. You cannot do an update over wifi as your version of iOS predates the introduction of over the air updates.