software update Ios

You also have a lot of Other storage that may be able to be released

You can try rebooting the iPad and see if it clears the space required form Other: link-> Restart your iPad - Apple Support

Or connect it to a computer running iTunes or Finder and update through there.

Link-> Update your iPhone, iPad, or iPod touch with iTunes - Apple Support

Link-> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Go to Settings->General->Software Update.

Do note it can only update to iPadOS 15.7.

Link-> Update your iPhone or iPad - Apple Support

The answer is right in front of you.

You have 2.7 GB free space. The update requires more than that plus some additional overhead. Think 5 GB minimum.