The Original iPad can only be updated to IOS 5.1.1.
(a) Hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears
(b) Double-click the Home button, hold the apps down for a second or two until you see the minus sign. Tap the minus sign to close all the apps
The iPad 1 is Not compatible with iOS 7.
Are you sure yours is an iPad 1...?