Sure! Here are the rewritten sentences:

1. He advised me that I had better study harder for my exam.
2. They threatened me, saying that I should give them my suitcase or they would kill me.
3. She reminded me to remember to lock the door.
4. She advised me that I ought to read the question carefully.
5. She warned me not to put my hand on the oven because it was hot.
6. The doctor instructed her to take the medicine every night.
7. He warned me that he would punish me if I didn't go home on time.
8. He advised her that she shouldn't buy this house.