How can I change the text for a field of the subscription form in joomla? I don't want only "Name" standing there.
You can change this in the language file.
Go to Acymailing->Configuration->Languages and edit the corresponding language file. In the Custom Translations panel add this line: ACYM_NAME="Replace this string with whatever text you want" and save your language file.
Here's the documentation: https://docs.acymailing.com/setup/available-language/translate-acymailing