You either need to locate the email with your Game Dev serial that SMS sent you or go to your CP account. 

You don't need to download all the content installers again but you should download the main Poser installer and the support files.  The support files have all the documentation and updates to manual regarding the new tools for the Game Dev edition.

If you are still within the 30 day download time frame, you should be able to lauch the SM Download Manager, put in your Game Dev Serial and download the files you need.  When I downloaded it, there were two tabs in the DL manager window.  One had the Game Dev installers and the other had the SR 4 update and Pro 2014 content update. 

If you are beyond the 30 day download time, go to your CP account.  If you need to, you can click on the expired download links and it will take you through purchasing the extended download service. 

If you have the files and have them installed, copy and paste your Game Dev serial in the serial number box of the personalization box.  Your old Pro 2014 serial will appear in the old serial numbr box.  Fill in any other fields you want or need to and hit ok.  Then close Poser and restart it.  You will get a new start up screen that will list your Poser version as Game Dev rather than Pro 2014.  That pretty much indicates it's installed.