Thank you for contacting Telerik support.
There is a functionality in Sitefinity which allows you to replace an existing image with another one and is designed exactly for cases like the one you described.
To use this functionality:
1) Go to Content> Images and select the image you want to replace
2) Open the image to edit it. Right under the image you will notice a button named Replace image (see the attached screenshot)
3) Click the Replace image button to select another image then Save
Hopefully the image will be replaced everywhere.
Please try this and let me know if it works.
the Telerik team
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