npm upgrade with homebrew

Question

When node (v.0.10.33) is installed with homebrew (v. 0.9.5), at one point it says:

==> Caveats
If you update npm itself do NOT use the npm upgrade command
Instead execute:
npm install -g npm@latest

So, what exactly is npm upgrade and what is the difference with npm install -g npm@latest?

-- edit 2015

the problem doesn't exist anymore with the current version of node. (but I never had an answer to what npm upgrade is?)

Answer 1

Use npm install to install a package and npm update to update a package.

That Homebrew npm caveat was removed after the issue with npm update -g was fixed.