Categories can be manually assigned in two ways; via the product list view:
and also in the product edit view:
Both of these methods will present the same categorising dialog.
The category trees can be expanded through the caret to display additional category nodes.
Both individual nodes and parent categories can be selected to assign to or remove from a product within the same process.
Once the relevant categories have been selected, either 'Add' or 'Remove' can be selected to move the categories into the relevant field. 'Remove all existing categories' can also be selected to ensure that all categories selected to be added will be the only categories applied to the selected product. Selecting 'Categorise' will apply these changes.
Once a product has categories assigned to it, the categorise dialog will show the existing categories the product is assigned to. You are able to remove these categories from the product by selecting the red 'x' that appears when you hover over the categories on the right.
All categories can also be stripped from a product by selecting the 'Remove all existing categories' option.