I recommend performing an account back up in the first instance which would give you a zipped file containing .csv files of invoices, clients, bank transactions etc. This can be done by following the steps in this guide:
If you then wish to close the account, you can do so by following the guide below. However, as of the time of writing, we don’t currently close accounts or delete data automatically. If your account is unused, it’s likely it will fall into the free category (XS, S, M, less than 1,000 nominal ledger entries in a rolling 12 month period), if it hasn’t already. Should this change, we would notify you before taking any action.