I've improved an assignment. Can I submit this one instead?
This answer explains how you can upload an updated assignment if you're still within the deadline.
Answer
This depends. If the deadline for your assignment has not passed yet, then it's likely that you can.
To do this, you would just re-access the submission point on Brightspace and upload your updated assignment.
It might be that the course team have set the assignment to accept one file submission only. If this is the case (and assuming the deadline hasn't passed), contact them to see if you would be able to submit your edited assignment.