Replacing a cloned voice on my creative agent using the edit function

Hi there, I made my first creative agent and I'm happy with it but I think I can improve on the cloned voice. In my first attempt, I used a 30s iPhone read. However, I now have access to multiple good audio files of my own voice. So I went to edit my agent's voice with the new files and uploaded them to the platform. However, I kept being told I have reached the voice limit. Does this mean the edit function does not allow me to change out the voice of the agent? Do I have to delete the agent and start again? Or do I need to upgrade from pro to a higher tier to allow me to do this?

Looking forward to your answer.