Change the locks. You really don’t know who else has keys to your home, so change the locks. That ensures you’re the only person who has access. Install new deadbolts yourself for as little as $10 per lock, or call a locksmith — if you supply the new locks, they typically charge about $20 to $30 per lock for labor.
Here’s a video on how to install a deadbolt lock: https://youtu.be/VNX5MQZNWmk