Dears;
Is it possibke to download firmware update but not installing it straight away?

Sure!

I think you can get it via iTunes, but I've never done it that way. I've always gotten my firmware from here: Official Apple IOS Firmware Download Links for iPad. Just make sure that if you use Internet Explorer to download it from here, that you change the extension to .ipsw (IE will download it as a .zip file - and don't unzip it, either).

Regardless of where you get it - it's not a problem to download it to use later.

Marilyn