Once you have bought the add-on/theme and assigned it to your project/site you should be able to see a notification telling you that there are updates available under Dashboard > Extend Concrete5.
If you are not seeing any update notifications it could be one of these reasons:
- Your project/site is not linked to the Concrete5 Marketplace. Connect it via Dashboard > Extend Concrete5 at the bottom you will see the button "Connect To Community" or follow this instruction found here.
If you are still having the problem to connect follow this link for instructions.
- You have no license of the add-on/theme assigned to your project/site follow this link to know how.