Cannot make update. Version iOS 9.3.2, iphone 6s

Hello. Have an issue with iphone update. It's Iphone 6s and current iOS is 9.3.2. So no latest updates have been done for a while.. anyway I can not find how to make an update. Phone says: the version of iOS running [...] does not support wirelessly updating to this version of iOS. Please connect your device to iTunes on a computer to update to the latest software.

When connecting phone to iTunes, it does not give an option to download and install the newest version. It is possible only to press this button ''Check for Update'', it shows what version have the one and that's all.

iTunes shows message:

iOS 9.3.2

Your iPhone software is up to date. iTunes will automatically check for an update again on 2019.01.29..

Thank you in advance!