You may now sort products of the whole collection by drag and dropping them.
As a brand manager, head to the top navigation and click on "Collections", then choose the collection to manage, then click the "Sort products" button.
Access from the back-office collection page
Alternatively, you may browse to the Products page of your collection in the showroom and click the "Sort products" quick-edit button.
Access from the showroom collection page
You will then be able to sort products from the whole collection by easily drag and dropping them...
Sorting products with drag & drop
... or sort categories themselves (just switch mode by clicking the "Sort categories" toggle):