Is it a quill stem or a threadless steerer? I suspect the former due to the bikes age so it's just a question of releasing the quill bung and pulling the stem up. Be careful not to pull it up too far.
Depending on how far you want to raise it you might need longer brake and gear cables. Check you have sufficient slack in them by turning the bars lock to lock.
To release the quill bung you need to unscrew the bolt (C) that runs through the middle about half an inch or so and hit it down with a mallet. This will release the bung (D) in the steerer tube (B) and the bars/stem will be free to move in the head tube. When in the required position tighten the bolt to lock it.
Hello Josh and

to the forum.