The Accounts in Float are derived from the chart of accounts in your accounting package. As a result it's not possible to update the name or classification of the categories directly in Float, however you can update how these show in the cash flow.
If you click an account in 'Manage table layout' above the cash flow table on the Cash Flow tab, you will see the following modal.
Here you can update whether the account appears under cash in or cash out, and also whether it appears as part of a group (for creating groups click here).
The other option that exists is the option to remove the account from the cash flow. If a account is empty and contains no actual value from your accounting platform it can be removed from the cash flow. However if there is actual value associated to the account it can't be removed. On the right side of each category you will either see a trash can or a padlock, similar to below.
In the above example, 'Accounts Receivable' has value and is locked so can't be removed while 'Audit & Accountancy fees' has no value and can be removed by clicking the trash can.
If you want to add a previously removed account back into the cash flow or add a completely new category click here.