Check with your local library or schools to see if they accept book donations. If not, there are probably a few secondhand bookstores near you that will buy some of them from you.
This is the best way in my experience; I was able to get rid of over 20 filing boxes of books this way while helping my folks downsize their collection. It’s a small way to support your local library system, and I’ve had some excellent finds at thrift book stores/library sales over the years so it’s nice to contribute to that as well