How did Kanade get access to Angel Player?
From the Wikia:


  Some time after the creation of the Angel Player program, a student by the name of Kanade Tachibana discovered the program and became the first user of the program. She used the program to create Guard Skills to battle against the SSS.


(emphasis mine)

The exact details of the acquisition process is not revealed, however it is believed that Kanade found the program by herself. Considering that she has an English manual, it could be that she found it with one of the computers in the computer room, or bought it in the Afterlife.