OSX upgrade => brew update

Question

A Macbook was upgrade from yosemite to Sierra to High-Sierra. The feedback indicates that brew is configured for yosemite:

brew install members
Updating Homebrew...
==> Downloading https://homebrew.bintray.com/bottles-portable-ruby/portable-ruby-2.6.3_2.yosemite.bottle.tar.gz
######################################################################## 100.0%
==> Pouring portable-ruby-2.6.3_2.yosemite.bottle.tar.gz
==> Auto-updated Homebrew!
Updated 2 taps (homebrew/core and homebrew/services).

What is the optimal (preferably simple) technique to ensure that brew is correctly configured for High-Sierra?

UPDATE

I followed the instructions returned by brew doctor , which seemed to clear up many errors. (thank you)

Additional:

brew update Already up-to-date.

Users-Air:~ user$ brew install members

Error: No available formula with the name "members" ==> Searching for a previously deleted formula (in the last month)... Error: No previously deleted formula found. ==> Searching for similarly named formulae... Error: No similarly named formulae found. ==> Searching taps... ==> Searching taps on GitHub... Error: No formulae found in taps.

Users-Air:~ user$ members

-bash: members: command not found

Answer 1

brew doctor is always your friend on healtchecking your homebrew installations.

[update]

I could not find members formula either.

$ brew search members
No formula or cask found for "members".
Open pull requests:
hugo 0.70.0 (new formula)  (https://github.com/Homebrew/homebrew-core/pull/57334)