How can I update my mid 2010 Mac to Sierra is?

If your mid-2010 iMac is running Snow Leopard, upgrade to 10.11 El Capitan first, then Sierra. Make sure before upgrading out of Snow Leopard, you don't need older PowerPC applications like Appleworks.

https://discussions.apple.com/docs/DOC-8811

FWIW, High Sierra 10.13.6 is the latest version of macOS you can run.

How to get old versions of macOS - Apple Support

You can't

Late 2009 iMac and later can upgrade to High Sierra, but there is a specific migration path they need to take*:

http://www.macmaps.com/docs/DOC-13695/

*Links to my pages may give me compensation.