Hi RosaAnna!
I'm glad that you're interested in the ProAdvisor Certification program. I'm happy to provide information about it.
You won't need to upgrade your plan, but you need to sign up for a QuickBooks Online Accountant account. It's free, and it's where you can take the exam. I recommend taking the training modules first, but you can skip them and proceed with the exam if you want to.
To take the exam:
- Go to ProAdvisor on the left menu.
- Select Training and choose Certification hub.
- Click Take exam.

You can also check out this article for your additional reference: Frequently Asked Questions about ProAdvisor training and certification.
Feel free to comment below if you need more help. Take care and more a good one!