Go to Setup > Image Assets > Event Icon and Poster
The dimensions for the Event Icon are 120 x 120 pixels and for the Event Poster 640 x 744 pixels.
The maximum allowed file size is 1MB, and supported file types are: PNG, JPG, and JPEG. Images are required to be in a RGB colour space to display correctly in our apps. CMYK images will be automatically converted, however this can result in a slight colour shift. To avoid this consider converting CMYK images to RGB before uploading.
To add these images, click on Select Image and navigate to the location of your image on your computer, then click Open.
Once you have added your images, click on Save Changes at the bottom of the screen.