iPad shows software update available, but iTunes says none

I am trying to work out if I can update an MR6N2X/A Ipad running 12.1.1(16C50) software. the ipad says that there is an update available but when connected to computer (itunes) says that there is none available.

Q;

• it there an update available
• what is it
• how do i download to install

thankyou