Hi Tony,
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.
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This will update your company logo across your account including in statements and the standard invoice themes.
I hope this helps.
Richard