What computer operating system is your Premiere Elements 12 going to run on? After you install 12, please do not forget to install the 12.1 Update using an opened project's Help Menu/Update.
An external DVD CD burner is relatively inexpensive and could be a worthwhile addition to your computer resources as n2deep suggests.
If you have any problems with the download of installation files as per John's suggested route, please consider the following web site as the source
Major thought for this route, you need to read and carry out carefully the "Note: Very Important Instructions" on the web page in order to avoid an Access Denied message.
These are Adobe tryout files into which you can insert your purchased serial number during installation.
Please review and consider and then, when you have the time, update us on your progress.
Purchase an external DVD / CD drive. They are very inexpensive and your need for it will continue.