It's obvious that you happen to re-upload the same photo unknowingly, but no need to worry about it as you can go ahead and delete the photo that you wish not to be there in your portfolio.
To delete the image follow the below steps:
login into the Artist panel.
Go to Edit profile - portfolio.
Select the category where you have uploaded the image and scroll down. There will be a "delete" button option below the image.
Click on the delete button to remove the image from the portfolio.
Need help? Contact the support team via your artist panel by clicking on the support button.