Remove the tree from the pot by giving it a little tap on the edge. Tease out the roots of the tree and then place the tree in the middle of the hole. Backfill the hole with your existing soil so it just covers the potting mix. Then compact your soil so there aren't any air pockets within the hole.
Following the instructions on the pack, add seaweed extract to your watering can and drizzle on the plant. This will reduce transplant shock and help the roots to establish faster. Then spread 5–10cm of mulch around the base of the tree. This will help the soil to retain water and insulate the tree in winter.