When the Basic accounting type is selected, access is restricted to change from Basic to Advanced. These are the steps for Firefly team members to assist with an accounting type change.
1. Get the parks acknowledgement and acceptance of accounting changes.
The following information must be acknowledged and accepted by the park before the accounting type is changed:
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Cash-based information will be deleted when the accounting type is changed. All cash-based data you wish to keep should be printed or exported prior to the change.
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All previously posted batches will need to be reversed and reposted. This will allow deposits currently recognized as revenue to be recognized as deposits and will create accurate reports.
The above bullet points are copied from a snippet in HubSpot. Sending the snippet allows for email documentation of the park's acceptance... https://app.hubspot.com/snippets/21079145/edit/3542239?q=acc&page=1
2. Remove restriction for Accounting - Advanced (Hybrid, Accrual) in Account Manager.
Both accounting features above must be unchecked - so they are not restricted.
No restrictions on Advanced allows Hybrid and Accrual to appear in Accounting settings. 
No restrictions on Basic allows the Accounting dropdown to appear in Firefly's main menu. This dropdown is where users access End of day and Posting Batches.
Individual user access to the Accounting dropdown is shared in user permissions, but the dropdown will not appear for any user if the feature is restricted in Account Manager.
3. Change the accounting type.
Firefly staff can do this but the park also has access to do it themselves.
Go to... Settings > Accounting > General Settings > Accounting Method > Save
4. Reverse and regenerate any batches previously posted.
This step is essential for reports to accurately reflect revenue data.
Go to... Accounting > Posting Batches > select batch > Reverse Batch > repeat until cleared
Now, generate the batches again to create revenue history for the new accounting method.
Be sure to generate both Payment and Transaction batches.
For more information on the End of Day process or errors encountered, see these articles...
Accounting End of Day Procedure
There are errors on my End of Day update!
5. Congratulations, YOU'RE DONE! 🎉