What program are you interested in - Photoshop Elements 13 or Premiere Elements 13 or both?
The word "upgrade" that Adobe refers to is for pricing only...if you show proof of purchase for an earlier version, you can get the product at a lesser price than if you did not purpose a program before.
Photoshop Elements and Premiere Elements versions are standalone products. So,
a. You can purchase download installation files and serial number from Adobe (where "update" pricing would be available)
b. You can purchase elsewhere and be governed by the pricing of the authorized reseller. Sometimes the pricing of the reseller can be less than the Adobe "upgrading" price. Shop around and compare prices online.
Please let us know if you are OK with the above information. If not, please let us know what supplemental information that you need.
This is not Adobe. Rather user to user.