You go to the jam site https://itch.io/jam/cga-jam, and find the Submit button. You can submit games from the beginning of the jam till the end. Hope that helps!
This is an example using another jam:
If you have not join the jam yet - http://imgur.com/ATz8pVQ
If you have already joined the jam, submit here - http://imgur.com/o9NLxu9