Change Image size on current entry?

You have to do it the "long" way.

Withdraw and re-enter. If the challenge is getting close to full, get your replacement image loaded to your gallery first to speed up the replacement time.

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/A veteran is someone who, at one point in their life, wrote a blank check made payable to their country for an amount of "up to and including my life"./
(...from the generation that still uses capital letters and punctuation...)