First, we'd like to inform you that we are not able to reactivate deleted MuseScore accounts so, think twice before you do it.
In order to delete your MuseScore account, you need to perform the following steps.
Log in to your MuseScore account on our website https://musescore.com/. Click on your username in the upper right corner of the page. Go to "Settings" and click "Delete account" on the left of the page. Confirm by clicking on the "Delete account " button.
Now your account has been successfully deleted!
Please note that deleting your MuseScore account doesn't prevent you from charges if your trial subscription was set up via AppStore or Google Play.