Note: The maximum file size that can be uploaded is 32MB.
Here are the recommended sizes for each place you'll find to add a graphic:
Header Image (AKA Hero Image): (W)1080px x (H)400px
Sponsor Graphics: (W)172px x (H)120px
Promo Grid Thumbnail: (W)600px x (H)600px
Share Image: (W1200px x (H)630px