updating nodejs on ubuntu 16.04

I was recently going through the version of node in my ubuntu 16.04 when `node -v` command was used it shows me version 6.9.1 but when `nodejs -v` it shows 6.9.2 previously before using this commands `npm update` command was used. Now what's these difference in `node -v` and `nodejs -v`? and how to update to the latest LTS version of node/nodejs?