How do I pick which chapter titles to change after Retitle has read my chapters?

From version 1.9.24, the Retitle window shows each chapter's title "Now" and the "Proposed" one side by side. Under the current title it says "Fits" or "Does not fit", and under the proposal a short line says what the chapter is about. The chapters whose title does not fit are ticked for you. Use "Tick all", "Only those that don't fit" or "None", or tick chapters one by one, and edit any proposed title in its box. Then press the "Rename" button, which says how many chapters it will rename. The chapter list, the contents page and every export use the new titles. While it is reading, "Stop and review what was read" lets you review the chapters read so far.