It doesn't matter how you initially installed it, the script can be used to upgrade. In fact one of the common usages is to recover from installations attempted using other techniques such as installing using apt.
the script does not work for me with raspi 4 and buster - any idea why ? am I doing anything wrong ?
pi@raspberrypi:~ $ sudo curl -sL https://raw.githubusercontent.com/node-red/linux-installers/master/deb/update-nodejs-and-nodered
pi@raspberrypi:~ $
Best to stick to your original new thread you opened 
