Free trial to what? Where did you buy the serial number from?
i had the free trial of photoshop element 13 .... I liked the program and bought it on the black friday sale they had online off the adobe website
then they emailed me the serial number and i registered it an all on the website. it says if converting from free trial you do not have to redownload it to the computer to just type in the serial number when you sign on to the program... i select license this software...and type in the serial number, and its says it is not the correct number for photoshop element 13.