To upload a company logo to your system:
Click on the 'Settings' tab
Select the 'Company' tab
From here, you can click 'Browse' to upload a logo from your desktop files:
You should upload a high quality image. The height must be 28px for the best effect (28 x 28px for square or 300px by 28px for rectangle). Re-sizing an existing image would stretch this so the image would need to be designed at this proportion.
The image should be visible on a dark background. Your logo will be shown on your login page. Make sure the image looks good, as this is the first screen your employees will see.