Pull the awning down, set the tension rafters.
Have a step ladder handy, about the height of the awning not elevated.
Remove the 1/4 x 20 bolt from the REAR elevation arm, CAREFULLY as it's under tension. Keep hold of this arm. Leave the tension rafter set.
Support the roller tube on the step ladder, or have someone rest it on their shoulder.
Rotate the loose elevation arm 18 turns counterclockwise, this will unwind the tension in the awning spring.
Reattach the elevation arm.
Manually roll the tube to it's top position.
Remove 2 screws from each end of the slat casing, each on the same slat.
Slide the slat out of the casing
Tape the awning up so it won't unwind.
Lower to the ground and remove the ends from the tube.
Find an 18' table to work on it, now you have the roller tube of the trailer.
When you replace the fabric do not attach the rivets holding the fabric to the tube until you have the awning back on the trailer and extended.
Once thats done you will need to wind the spring 28 turns, (when you install a new awning it winds itself 10 turns as you roll it down)