Most banks will only provide the last 90 days of transactions online so you would have to go to you banks site and export the older transactions to a QBO or OFX format file.
Once you have the file go to the bookkeeping section, click the small 'cog' on the right and click on import transactions. This dialog will ask you for the account you want to import into and allow you to choose the file to import.
Please double check the dates of the transactions you are downloading to make sure there is no duplication of transactions already loaded, 17hats doesn't check for duplicate transactions at this time.
Keywords: Bank Account, Transactions, Import