Closing an Account -

If you have closed an account or you have an account you no longer use - you can mark it as “Inactive”. This will prevent it from being shown within drop down menus in account registers, or being synced with your mobile devices.

To mark an account as inactive, select your account then navigate to Account > Edit Account. 
Enable the “Inactive” box.

This item is distinct from the “Hide on Summary Page if balance is zero” option.

Inactive accounts are still accessible from reports, and can be unmarked as Inactive (i.e., returned to active use) at any time.

Hiding an Account - 

To remove an account from the left sidebar, highlight the account name and right click (or press Ctrl and click). Then select 'Remove from Side bar' to remove the account from view.

Should you wish to re-add an account, you can select the '+' button at the bottom left of the side bar. In this window you can highlight the account name and select 'Add'.

Selecting 'Advanced' will expand the window, making it easier for you to add and remove multiple items at once.