You are not obligated to update. I am using a previous version as well, and everything works fine.
But if you want to update check this link: https://devcenter.heroku.com/articles/heroku-cli
It says that to update your heroku cli you just have to do this:
heroku update
But there is this issue:
Not all methods of installation are updatable with heroku update. Apt users will have to use
sudo apt-get update && sudo apt-get upgrade heroku
. npm/yarn users will have to update with npm upgrade -g heroku-cli or yarn global upgrade heroku-cliIf updating does not update the CLI, try uninstalling with the uninstall instructions below