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You might consider removing that same amount off the bottom where a joint line would not be as visible. Don't forget there will be internal side panels that need to be shorted also. The back and the front and the ends will be the easiest, but the interior panels my require a hand saw or a sabre saw. A guide board should be use to keep the cuts from wandering when using your circular saw with a 60 tooth blade. I have reduced the depth of some Hickory cabinets, but never needed to reduce the height of one. A Japanese pull saw may come in handy for the corner cuts.
Good thing it's a painted cabinet, you can touch up any flaws easier.
The doors may also present an issue if you want to shorten them, it's certainly doable, but a bit more work to take them apart.... if that's even possible. Give it a try since you've partially committed to buying new anyhow. Test your skill on these....
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 01-23-2020 at 05:53 PM.