Can I upgrade from ios 6.0.1 to ios 8.1.1 directly?

Please help me quickly! I have some problems that I have iPad 2 wifi. I want to update ios 8, so, I buy ios 8.1.1 for ipad 2 wifi ipsw. I update with itunes PC but it showed that it cannot update my ipad! Why is it? I want to install ios 8.1.1 but current version is 6.0.1. Why can't I upgrade it? Please help me!!!!!