Learn more about Shift's pricing plans here.
If you've just upgraded to Shift Advanced, it should automatically update your account for you fairly quickly. Make sure you are signing in with your primary Shift account to see your paid features. However, if for some reason your upgrade isn't taking effect right away, try quitting Shift from the menu bar and re-opening it to speed up the process.
If your menu bar is not visible go to Settings > General > Appearance > Show app menu to enable it.