Updating iPad without computer

only very old versions of ios are unable to upgrade on their own

if you have older the ios 5 https://www.iphonefaq.org/archives/971646

then you can upgrade without a computer Update your iPhone, iPad, or iPod touch - Apple Support

if you have a lower then ios5 version you need to use the computer of a friend and or relative, public library or store computer with iTunes installed on it to upgrade

If it is saying it is disabled and needs to be connected to iTunes, then your only option is to find a computer with iTunes to use to restore it. There are no other methods at that point.

If you get a message that you need a computer to update the iPad, then you must use a computer. Where are you seeing this message?