In order to download the latest version of the Store Manager software please use the blue button (or green arrow) at the top left corner of the Store Manager software.
Also worth mentioning that you will have access to the latest version of the software within 6 month from the date of your purchase. Within this period of time you may update your Store Manager as many times as you want.
If you like you can prolong update period by purchasing Update and support services.
Order Update and support Service for 6, 12 or 24 months for PrestaShop here.