People ask this question quite often as probably there's no quick shortcut from Kanban Board/Task board to the screen where customization is done.
Now, let's see how we can change/add states for User Stories in Kanban board. The key to customizing columns is essentially changing states for User Stories. So, here's our Kanban board:
We've got 5 states for User Stories in there: Planned, In Progress, In Testing, Analysis, Done. Let's suppose we want to remove Analysis column and replace it with Ready to Merge Column.
We need to go to Admin-Processes, and select the Process used for our Project (Kanban process in our case). Then we go to Workflow for User Story:
All of our existing states for User Stories are in there. Let's now edit the states - replace the Analysis with Ready to Merge State:
Don't forget to click Save in the Add/Edit Entity State window, then Save Workflow.
Now let's see what happens with the columns in our Kanban board:
Ready to Merge column is right there!
This works the same for Task Board. You need to add/edit/remove states for Tasks in Admin-Processes-Task-Workflow-Change State to customize columns in Task Board.