Can I ask if you intended to post this issue in the Praise section of the community? I can move it to the Questions section if you feel it would be more appropriate there.
You can change your company logo globally from the Details screen (Settings > Organisation > Details). Select the Logo tab and click the Upload a logo button to upload your new logo. Click the Save changes button to submit the changes.
This will update your company logo across your account including in statements and the standard invoice themes.
I hope this helps.