how to update new macOS version?

See thee compatibility section of How to upgrade to macOS Big Sur - Apple Support

If your Mac is compatible with Big Sur, that also has upgrade instructions.

If not, see: How to get old versions of macOS - Apple Support

What computer are you running? Specifically, what year was you’re computer released?

(Year requirements for Mac OS 11.1 Big Sur)

See https://support.apple.com/kb/sp833?locale=en_US for more info