It is likely you need a set of removal keys. They are typically just bent pieces of metal that one inserts into a slot between the actual head unit and the trim fascia around it. You can then pull out the head unit from the rectangular cage that holds it. The cage itself is typically mounted by bending tabs around the dash (or in your case, wood) panel the unit is mounted in.
If you don't have a manual, google the model number to find one. It should describe the installation and removal process. If you don't have the keys in a bag with the manual, you can probably find some on eBay.
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2002 Classic 30 Slideout -S/OS #004
2013 Dodge 2500 Laramie 4x4 Megacab Cummins