You can easily change the logo of your business by following this guide.
1. First go to 'Setup'.
2. Click on 'Business'.
3. Now choose 'Business Details'.
4. Here you can find contact and address information.
On the left, below 'Basic Information', you can find an image of your current logo.
By clicking on it, the dialog window below is open, where you can choose an image for your logo.