1. He opened the window because he wanted to let fresh air in.

-> He opened the window in order to let fresh air in.

2. I took my camera because I wanted to take some photos.

-> I took my camera so that I could take some photos

3. We filled the car up because we didn’t want to run out of petrol.

-> We filled the car up in order not to run out of petrol.

4. I didn’t want to see them, so I didn’t open the door.

-> I didn't open the door in order not to see them.

5. He did not want to worry her, so he did not tell her what happened.

-> He did not tell her what happended so that not to worry her.

6. Tom was playing very softly so that he wouldn’t disturb anyone.

-> Tom was playing very softly in order not to disturb anyone.

7. The boy tiptoed into the room so that he wouldn’t wake every body up

-> Tom was playing very softly so as not to disturb anyone.