iPad Pro 13-inch return and exchange for 11-inch

I purchased an iPad pro 13inch yesterday 4th of Jan can I return it and exchange for an 11 inch instead? I have set up the 13 inch..but that all . Also purchased the 13inch keyboard and would like to replace same with an 11inch. What happens to the excess amount if exchanged? Thank you.

[Re-Titled by Moderator]