Updating to Professional or Master Collection.
If you have already been using GameMaker in some license form then you can easily update it by opening a project and selecting Help -> License.
Alternatively, if you are using a YoYo Account, you can log in and add a new license key and then assign that to be your primary license. The next time you log in to GameMaker it will update your version for you.
Adding a Module onto your Professional license.
If you have purchased a Module on it's own then you can create/use a YoYo Account. Once in your account, you will want to select license and then insert your license keys.
When inputting a Module key and you have multiple Professional licenses, it will give you the option of which one you want to enter it too.
You can check which modules have been added by Locating the Help tab and selecting About GameMaker. This will also let you know which version you are on. Alternatively, you can log in to your account account and find this out as well.
If you purchase a module at a later date, the above process to update your license must be carried out again to activate the new module inside GameMaker.
More information about the YoYo Account can be found here.
If you are still facing problems seeing any of the above then please contact the HelpDesk and we shall look into your issue.