How do I upgrade mac mini {mid 2011} from OS Maverick to OS 10.12.6?

A Mid 2011 Mac Mini can and for the latest security updates, should be upgraded to macOS 10.13 High Sierra.

see > How to upgrade to macOS High Sierra - Apple Support

Hello,

What is your Macintosh’s exact model number and what version of the system software is it running?

Choose the Apple Menu  > About This Mac