well it would depend on what shell you are using. a quick google search shows this:
For bash shell:
export PATH=$PATH:/usr/sbin/:/usr/local/bin
For tcsh or csh:
set PATH = ($PATH /usr/sbin /usr/local/bin)
That will let you set it in your current session. that basically says "set the PATH variable to what it currently is plus these two new directories."
if you want a more permanent change to it, you will probably have to edit your profile. in the tsch, it should be in your home directory, and is called '.cshrc'. There should be something similar for bash and other shells.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors