You can add your own company's logo to the Bitrix24 account. This option can be found in the Settings option in the left menu.
Scroll down the page to the Company logo section. Click the Upload button. Please note that your logo must be a PNG file with the maximum dimensions of 222px x 55px for standard logo or 444px x 110px for High DPI logo.
Remember that you can always delete logo and upload a new one if necessary.
The uploaded file will be displayed as your company's logo in the left top corner for all Bitrix24 account users.