Tell us how far you have got; so we know what bit you are stuck on!
There are a few approaches. It helps to pull the seat an inch or so towards the front of the van before trying to raise the back of the seat. That is done by either sitting on the seat, operating the handle nearest the door and walking the seat forward or sitting in the drivers seat, operating the handle and pulling the seat towards you (my favourite method). If the seat is a little reluctant, you can also pull it from the area where the seatbelts plug in.
New seats can be a little reluctant the first couple of times so make sure you are pulling the handle up enough for it to disconnect. If unsure, try "rocking" the seat backand forth a couple of times.
Now to raise the back, there is a webbing strap/loop in the gap between the seatbelt things (what are they called...?!) you may need to reach in and rummage! If you can't find it, slide your hand down the back of the bottom of the seat and pull - the sholw bottom of the seat will tip up (hinged at the front) to allow access.
When you pull on the loop, the back should pop up. On ours, a little pressure applied to the rear of the bottom of the seat is enough to pop it up.
Then pull up the handle, push the seat back. Jone done.