Good evening, @ErinKatz ...
- Can I increase the course quota above 500mb for a free-for-teacher account?
No. There is a max of 500 MB per course for file storage in a Free For Teacher account.
- Is the quota per class or for all my classes?
It is per course. See the first table in this document for further details: Canvas free for teacher account comparison | Instructure
- I am trying to import a class that is 850mb. If I can't increase it, can you give me a tip about what is making it so big so I know what to delete?
You can export your current course which creates an *.imscc file for you to download to your computer. Then, you can change the file extension on that file from an *.imscc file to a *.zip file. Next, unzip the *.zip file, and you'll be able to see a bunch of folders/files. You can see the HTML content pages along with other files that were part of the course that might be large in file size. This might give you a clue on what files might be causing the 850 MB size.
How do I export a Canvas course?
Hope this will help a bit. Sing out if you have any other questions about this...thanks!