01) Access the Control Panel

02) After login click on Layout >> Select template Active >> Click on the EDIT button

Select in the line: Left Side Menu Type

After clicking on the UPDATE button

03) You can also configure it in the Control Panel >> Configuration >> Categories and Subcategories Settings >> Full Categories and Sub-Categories or Drop Down Categories

04) You can customize the source code of the menu as desired by the Control Panel >> Layout >> File Management >> open the includes / boxes folder >> edit the files named categories.

Check the templates folder for the selected layout edit the file column_left.php to check which file to edit the menu on the left side according to the option selected in the Control Panel.