Other people probably do it differently, but you can try it like this.

1. Save your layered file (psd or layered tif)
2. Save a flattened version (file>save as>jpg at the highest quality)

Working with the jpg file:
3. Edit>Image Size> Change from 12"x12" to 8"x8"
4. Edit>Canvas size> Change from 8"x8" to 8"x10"
5. Save this version for printing (like before, change the name)

Make sure you tell the developer that you are printing an 8x8 image on an 8x10 print size so they don't do any additional cropping. Also make sure that your image is still at 300ppi for the best print possible.

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Colleen in Friendly Manitoba...
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