@emelie
To upgrade an existing Google Tag Manager (GTM) account to Universal Analytics, you need to follow these steps:
Once you have completed the upgrade process, you will need to update your tracking code on your website with the new Universal Analytics tracking code. You can also use Google Tag Manager to deploy the Universal Analytics tracking code on your website.
Note: Make sure to test the new tracking code to ensure that it is tracking the correct data before deploying it to your live website.