Here's why it's so difficult and what's involved:
* Attachment: The high top is likely bolted, riveted, and possibly even welded to the van's body. Simply unscrewing a few bolts won't suffice. You'll need to access all fasteners and carefully remove them without damaging the van's roof or the high top itself.
* Structural Integrity: The high top contributes to the van's structural integrity. Removing it will leave a large opening that needs to be properly sealed and reinforced to maintain the van's structural soundness and prevent leaks. This often requires welding.
* Safety: Working at height is inherently risky. You'll need proper scaffolding or a lift to safely access the top of the van.
* Wiring and Plumbing: The high top might contain wiring for lights or ventilation, and possibly plumbing for air conditioning. These need to be disconnected carefully and safely.
* Expertise and Tools: You'll need specialized tools like drills, rivet guns, welders, and potentially cutting tools.
In short: This is a job best left to professionals with experience in van bodywork and modifications. Attempting it yourself could result in damage to the van, injury to yourself, and a poorly executed outcome. Contact a reputable auto body shop or van conversion specialist to get a quote for professional removal. They'll have the expertise, tools, and safety measures in place to do the job correctly.