Whilst updating nodejs and npm on a Centos 6 or 7 server running Apache, I hit a few walls and as a matter of process found some commands that are handy to run before doing a deep dive in Google.
Cleaning the cache
sudo yum clean all rm -rf /var/cache/yum/*
To make the cache
sudo yum clean all; sudo yum makecache
If you want to run several commands use semi-colon as noted above.