Before you start moving things around, get someone to check your trim. The hull’s seam-line should be parralel with the surface of the water when you are sitting in a good (slightly forward) paddling position. If you decide to move it, you will have to change your foot outfitting as well, to allow your whole body to move forward in the boat. Sometimes a stern-heavy boat can be corrected just by sitting forward more, and/or cranking your backband up a bit.
If you need to move the seat, there are two seat bolts that hold the seat in it’s current position. They are the large screw-heads that are just outside the cockpit rim, right at your hips, when you are sitting in the boat.
Loosen (don’t take them all the way out!!) them each a couple of turns and give them each a nice "tap" with a hammer. You should be able to slide the seat now. If not, you sometimes have to reach in and give the seat a few whacks, in line with the central pillar that runs beneath the seat.
In a short boat like the Vision, an inch can make a huge difference. Get someone to check your trim again before you tighten everything down.