If your school is now hosting a Canvas account, then they will create your user account for you, there will be nothing you need to do except log in.
However, I suspect you are asking how you can move your content from your Free-for-Teachers account, into your new school account. You can easily do this, but you will not be able to move your enrollments nor any work they have completed. I would strongly suggest you have a nice long chat with your school's Canvas Admin/Support department to find their preferences in how the school would like this managed.
Anyways, you can create an export file for each course you have created in your own Canvas Account, then import those files into your new school hosted Canvas account. You will need to have your school create empty course shells for you to upload your content into - again, back to having a conversation with your elearning folks. The guides below will describe how to move your content.
There are some huge advantages to working in a school's Canvas account, and I think you are going to like it once you get things all ironed out.