Can I change the lock after my tenant moves out if she hasn't given me the keys yet?

Question Details:

My tenant gave a 30 day notice stating the last month will be her last in the house. She sent me a text stating that she wouldbe moving out on the 30th, and would be finished at 7 pm. I asked my son to go pick up the keys. He got there at 6:45 pm and left at 8:30 pm. The tenant never showed up. He looked in the window and saw that she still had things in the house. My son and I called her and sent her text messages but she never responded. She still owes me back rent for 2 months and now she has the keys to the house and garage. Important Notice