if you are the website owner, the owner of the domain name and the owner of webhosting account—you ultimately control your stuff. it will require some access into areas of your webhosting account and possibly the database to change the permissions.
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i know every situation is unique– however, speaking as a person that works with business owners to create their websites, I would (humbly) suggest that a different approach would be to resolve any issues that are standing in the way of the “web dude” setting you up with full admin user permissions. hopefully any issues are simple to resolve.
(for my clients, after i am done and paid for the work we have contracted for, i turn over all of the access. it is up to the website owner to grant access to me for future assistance as needed. )