If you are trying to update npm modules, you can do it by loading the Bitnami console and then run
npm -g install npm.
From the thread that you posted, it is mentioned that you can upgrade NodeJS and that it will be installed out of the Bitnami installation dir. In order to use that new NodeJS version, you need to follow the steps from Jota in the post linked below
If so, it’s not safe to copy the stack folder to another server?
If you follow the steps in that guide about doing a backup and then you migrate it to another server, then it will (by default) use the NodeJS version included in the installation directory, unless you perform the steps that Jota mention to use the system version instead.
Hope it helps,