I was wondering how I could make changes on a person's "Life Summary" section?
Are you talking about the Life Sketch added on the Details page of the individual? If so , when you click on it , you can make a change, as long as you state your reasoning. If you are talking about the section reached by click "Go to new Discovery Page", you cannot edit that section, but you can make changes to the Details of the individual in Family Tree, and it will be updated in a couple of weeks on the Discovery page.
The Help Center article about the Discovery Page says "Due to the delay in communication between the Family Tree and the discovery pages, it can take some time for the discovery pages to be refreshed after you correct the information in Family Tree."
Hope this helps.