I have macOS Sierra 10.12.6 on my mac pro, how i can get the security update that apple is recommanding this month

If it's a Mid 2010 MBP, the highest you can go is...

macOS High Sierra - Technical Specifications

General Requirements

• OS X 10.8 or later
• 2GB of memory
• 14.3GB of available storage to perform upgrade*
• Some features require an Apple ID; terms apply.
• Some features require a compatible Internet service provider; fees may apply.

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac. These Mac models are compatible with macOS High Sierra:

• MacBook (Late 2009 or newer)
• MacBook Pro (Mid 2010 or newer)
• MacBook Air (Late 2010 or newer)
• Mac mini (Mid 2010 or newer)
• iMac (Late 2009 or newer)
• Mac Pro (Mid 2010 or newer)
• Don't use FireFox for these links…

macOS High Sierra - Technical Specifications

https://itunes.apple.com/app/macos-high-sierra/id1246284741?mt=1

I would add that depending on which newer OS can be installed, if it turns out to be an older one that is no longer supported, you could use a different browser such as Firefox which can be updated individually. Also, keep in mind that some OS upgrades can make some old 32 bit apps no longer functional and those will need to also be updated which may result in some costs.

Sierra is an old operating system and is no longer supported, hence no updates will be issued. You might look at upgrading your Mac's OS if that is possible.

Can you please let me know what you updated to? I am in same situation. My MacBook PRO 2010 works great..i need an OS