How to edit a board?

You can edit an existing board at any time from its Settings - Board Editor panel:

The pencil icon under a column or swimlane name allows to change its properties, the split-fork icon divides a column into sub-columns, and the bin icon deletes the column (you will be asked what should be done with any cards currently in it). The right, left, up, and down arrow icons allow you to change the order of the columns and swimlanes.

Please note, board settings are not accessible to all account users. Team members, who can access settings are those, that were given at least a project manager privilege or were made a board owner.