You'll be able to replace the Paperless Post logo and branding for all Cards and Flyers from your Create page. To do so, you'll want to click "Header Logo" on the left-side menu:
From there, you'll be able to upload whatever logo or image you prefer. You can use any PNG, JPG or TIFF file under 20MB, though we recommend sizing your image to 300x300 pixels for the best display.
Once you add this, if you haven't already, you'll be asked to upgrade your event to the Paperless Post Plus feature bundle for 200 Coins in order to save.