GMC Sierra Classic 2007 Owner's Manual page 204

3. Remove the three bows by gently pushing
them against the spring-loaded end. The
three bows are labeled front, center and rear
to remind you of the order in which to
reinstall them.
204
To clean the tonneau cover, use mild soap and
water. If necessary, use a soft bristle brush
to remove dirt trapped in the grain of the material.
4. To add cargo to the
box, remove all
bows and the back
rail and stow
them safely.