texlive manager (tlmgr) is, by default, a shell (or Windows terminal window) command. There is voluminous documentation about it from the command
tldoc tlmgrbut basic operation is pretty straightforward. The manager needs to know where to download stuff from; the canonical setup is
which passes the decision to the mirror selector. You can (of course) specify a particular archive or mirror that you “trust”, or even a local disc copy that you keep up-to-date (disc space and bandwidth are so cheap nowadays, that a “home mirror” of CTAN is a feasible proposition).tlmgr option repository http://mirror.ctan.org/systems/texlive/tlnet
To update a single package, use:
tlmgr update
To update everything you already have in your installation, use:
tlmgr update --all
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=inst-texlive