Thank you for your question.
Actually Joseph was on the right track however depending on what series your door is, the procedure will vary. The Architect and Designer series will be different from the Proline series. Also you will need to take a couple more steps first to get the panel out. For ease of understanding and efficiency for you I have included a link below that will walk you through the process of removing the sliding panel of all the above mentioned Pella series sliding doors.
I hope this answer is helpful and thank you again for your question.