To set your company logo click the top "Gear" icon and from the drop down menu.
Next, click "Account" to manage your account settings.
Next within your account settings page click the "Company logo" box
A pop up will appear prompting you to select an image file from your local disk.
Select your logo file (Must be a valid image format jpg, png...).
After the upload is done click "Save" and you are all set.
When you generate an invoice, now your company logo will appear on top.