Hey @Thilo Wilmes and welcome to the community!
as Nic mentions the Premium or Standard tier of Jira does not reflect on to a person/user but to the product subscription itself.
If you change your subscription to a premium tier then your entire product is premium (this can be set by product if you have multiple on a single instance (JSM vs JSW)) and all the licensed users of that product will be "premium".
So the subscription level doesn't reflect on the user but on the product they are using. (like JSM or JSW Premium)