To modify the "Testimonials" section :
- From the dashboard area, Go to Testimonials > All Testimonials
- Find the "testimonial" you want to update and click "Edit", or, add a new "Testimonial" by clicking on "Add New" button.
You can also modify the section settings by going to Dashboard > Appearance > Widgets, in the "Homepage" section, you'll find the widget "Testimonials", click on the arrow on the right to open its settings.
For video tutorials covering this please visit: http://videostock.io/tutorials/features-testimonials/