how do i update my macbook pro 2016

You can update your MacBook Pro 2016 to macOS Monterey which it’s compatible with it , from this link scroll down and find Monterey 12 do click over that link and you can start from there the update

How to download and install macOS - Apple Support

Hi, abenaamissah, your MacBook Pro could be updated to Catalina… you’re on El Capitan which has no more updates for that… software update might not work for finding updates

to your current MacOS as Apple figures you’ll get the news about software updates/upgrades from the usual Mac news sources.. Appleinsider.com, Macrumors.com. 9to5mac.com, etc, so go to the App Store and look for Catalina.. note, however, that Catalina breaks all 32-bit app/ software support. All of them have to be full 64-bit+Catalina compliant to work….

John B