Update Node version for Meteor app deployed to Heroku - node.js

Question

I have a Meteor application deployed to Heroku. To prevent the Denial of Service (DoS) vulnerability, Heroku suggested updating the Node.js version
for my application. I want to update the meteor version to 1.2.1 and node version to 4.8.4 on Heroku. I have set the node version in packages.json as well but it was not updated after deployment.
How can I update meteor and node on Heroku? I tried the following command:
heroku run meteor update --release 1.2.1 -a myappname
but it throws the following error:
bash: meteor: command not found
Any help would be much appreciated.
Thanks in advance!

Answer 1

To update my application's node version to 4.8.4, I updated Meteor version to 1.5.1 on my local machine, fixed the dependencies issues and pushed code to the Heroku application which solved the issue.
I used the following command to update Meteor version to 1.5.1 which updated the node package version to 4.8.4 as well:
meteor update --release 1.5.1
After committing and pushing code to Heroku, there were a few babel-runtime and bcrypt crashes. I executed the following commands to fix those issues:
meteor npm install --save babel-runtime
meteor npm install --save bcrypt
meteor update iron:middleware-stack.
Pushing these updates to Heroku solved my issue.

Answer 2

You can use the following command to update Meteor version to 1.5.1
meteor update --release 1.5.1

Answer 3

Command like heroku run meteor update will not work because Meteor is not installed (and is not meant to be) in the Heroku environment.
It is used in the buildpack (assuming you use the Meteor buidpack horse) to build your Meteor project source code into production version. It then becomes a "standard" node app. The buildpack also reads the node version required by the project Meteor version (not the one specified in your package.json file unfortunately) and configures your Heroku environment accordingly.
The buildpack does everything automatically from your Meteor project source code, but that also means that it is tied to Meteor (which is also understandable because any arbitrary node version may not work with Meteor).