How to change category layout in Magento 2 ?

To change the category layout, go to Products -> Categories -> Select your desired Category  go to the Design tab and select desired option from the Layout dropdown. 

If you wish to apply the Layout to all categories and sub-categories, make sure that you have checked the Use Parent Category Settings for all sub-categories then on the parent category select desired Layout which will be applied on all its sub-categories.

To check refresh the frontend after changes and if necessary clear all Magento caches.