Open a request from the help screen saying which of the two you are exercising, the export of your data or the deletion of your account. It is handled by a person rather than a button, because deleting an account takes away access for every one of its members and nothing undoes it.
The export bundles company, members, campaigns, leads and ledger. Your leads themselves can be exported at any time without a request, from the Export link on your list.
Accounting entries and invoices are kept for the legally required period, even after the account is deleted. That is an obligation, not a product choice.