Within the Import link find the option to import all your products/categories.
Clear Existing Categories Before Import?: select this option if you would like to remove categories that exist currently on your site before you import new categories.
(Please Note: to import you must use either XML or CSV. We recommend using CSV, first exporting all your products/categories first using CSV, then edit the file and import that file).
Paste XML / CSV Here: within the text box paste the file then click the "Ok" button located at the bottom of the page.