To begin, use a fabric unpicker/seam ripper to remove the zipper from the cushion. You don’t have to unpick every stitch – just unpick every fifth stitch or so then rip the zip off.
Next, use fabric scissors to separate the two sides of the cushion cover by cutting up the remaining three sides. Now you should have two squares of fabric that are roughly the same size. Each square will be one curtain panel.
Give each square of fabric a quick iron (5 - 10 seconds per square is sufficient).
Now it's time to hem your curtains. Flip your fabric squares over so that the backside is facing you. Following the instructions on your brand of fusible tape, iron a strip of tape to the bottom of your fabric square.
Remove the backing tape from the fusible tape. Fold the fabric over and press. Repeat on two more sides, leaving one side unhemmed. Repeat steps 4 - 5 on your second fabric square.
Now it's time to create the rod pocket.
Still working with the back of the curtain facing you, iron a strip of hemming tape on the remaining unhemmed edge of your fabric square. Then, grab the curtain rod you intend on hanging your curtains on and lay it across the fabric.
Remove the backing paper from your fusible tape. Then, fold your fabric over to create a little ‘pocket’ that’s just the right size for your rod. Keeping the rod in place, run the iron over the fusible tape. When finished, repeat on the second fabric square.