How to remove the cover from the metal structure

1)With a knife or a pair of scissor cut the string attaching the canvas to the metal frame

 

2) With a pair of pliers, bend up the end of the metal track

 

3) Do it on both sides of the track in order to free the canvas.

 

Both ends of the track should look like this and the canvas should be free to pull.

 

4) Pull the canvas from one side.