A small stepladder or sturdy plastic bucket can be used as a booster. Or use the end of a corner flag pole to lift the net over the crossbar. Lock the lock on the lockbox when the nets are out for the games. Open locks seem to walk away. Nets fit better if you hang them inside the goal instead of draping them over the outside.
Nets have rope ties, either attached to the net or loose in the box.
Don't use tape to attach nets - it's hard on both nets and goals. For missing nets or locks, nets left up after games are over, lockbox damage, field damage, etc. Call a coach or another parent, or send a messenger to another field. The combination is the same at all fields. Don't call the AYSO hotline number - it is a managed answering machine, not a number somebody always answers.