Can I update an ipad 2 from ios 4.x to ios 7.x?

daal

Hi, I am considering buying a used ipad 2 that has ios 4 pre-installed, and I would like to know if it is possible to upgrade to a newer OS. I have read that ios 9 is too demanding for the old ipad 2, so I was thinking about upgrading to ios 7.x. I have seen on this site that firmware can be downloaded (http://www.iphonehacks.com/download-ipad-ios-firmware), but I haven't found instructions on how to install it. I am an apple newbie, and I have read that upgrading is not always possible - something about apple discontinuing signing... Can I upgrade or not, and if so, how do I do it, and which OS would people recommend?