1) you have to clear npm cache and then update bower
sudo npm cache clean
npm update -g bower
2) If 1st solution does not help
try to remove and install it again
npm -g uninstall bower
npm -g install bower
check if it is still here
which bower
if it will show you something like
/usr/local/bin/bower
then
rm <path from previous command>
and after install it again
npm -g install bower
open new bash window and enjoy latest version of bower
same will help with other packages
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