How do I temporarily remove section of vinyl fence?
In the picture of the interior, you can see the locking wedges (lugs) that hold the horizontal  beams in the posts. If you just pull out, the raised edge of the lug will prevent it.

One approach is to place a putty knife (or some other thin metal blade, not too sharp) inside the post, parallel to the beam, covering the lug and angled into the seam of the post's cutout. If there are two lugs, you need on on each side. The cutout should flex and let the lug pass.

You made need to cut down small putty knives to fit inside the post.

This assumes you have some starting point to move one of the beams horizontally.