Your Admin would normally set a company wide logo that will show on all quotes created by users in your company. If you are an Admin, the instructions on how to do this are HERE.
You can have another logo as an alternative by adding it as a default logo. The default logo will only apply to your quotes, however.
To do this, go to the print preview and click "Logos" at the top right. In the pop-up window, click on "Choose Image" and find your logo (it must be saved as a .JPEG or .PNG file). Set the dimensions and margins and press save.
To use the Admin logo instead, tick the "Use admin logo for this report type" button and save.