Dear @Auseli,
Welcome back to the Wefugees Community and thank you for your question.
Unfortunately, I am not an expert on the student/vocational training residence permits and have to make some research myself.
We had a discussion on this platform before in which we were talking about the possibility to change the residence permit in a situation like yours.
According to this table (by GGUA), however, it should be also possible to switch from the residence permit according to 16a to 16b - given the fact that you meet the requirements (for more information you may check this website by the German government).
To be safe, I would contact the immigration office directly and ask about your options.
I hope this helps and please don't hesitate to get back to us with any further questions.
All the best,
Meike