The ideal format for the logo is a Square format; and for the banner it is landscape format, ideally 1500x500pix.
Go to the admin menu of the left side of the page, you will see 'Profile' at the bottom of the menu.
Follow these steps;
1-Click on 'Profile' from the admin menu
2-Click on Logo section to upload your organization Logo. Or you can drag and drop in your logo.
3-Click on banner to upload your organization banner. Or you can drag and drop in your banner.
4-Please scroll to bottom of the page and click on 'Update' button to save your changes.