Nice!
Removing/fitting the struts is a ten minute job. Best do this before fitting the rack and easier to swap one at a time.
You will see a metal spring ‘C’ at each end of each strut. Use a screw driver to pull them away from the end. They may come completely off (but they don’t need to be), just make sure they don’t ping off and you lose them. Either get someone to hold the tailgate open while you pop-off each end of the strut from the ball-pin attached to the van body, or do the next stages one handed whilst holding open the tailgate. The struts won’t fall off, but will need a bit of a tug. WARNING - ALWAYS KEEP THE TAILGATE SUPPORTED - it will have insufficient support with one strut fitted and will fall.
Fit the new strut (wide diameter end uppermost) by pushing the ends onto the ball-pins. No need to take-off the ‘C’ clips. Twist the cylinder of the strut by hand to line-up the connection to the ball-pin. Once one end is fitted, open or close the strut by hand to adjust the length to get the second end to mate with the other ball-pin.