Hi
Not sure I understand exactly what youx're asking, but as admin. you should be able to go into your section editor's upload field, change the size of of any one of the existing thumbnails (or create a new one for the new size) and then click re-create. The new images are created from your original uploads.
If you create a new thumbnail, be sure to reflect that in your viewer page code.
Hope that helps
Jerry Kornbluth
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