The old testament is full of good examples of people demonstrating free will. Adam and Eve might be the two best known old testament people that demonstrate free will. God placed them in the Garden of Eden and told them not to eat fruit from a particular tree, and both Adam and Eve willfully chose to disobey that command. Noah willfully chose to build an ark. Abraham willfully took his son, Isaac, up the mountain to be sacrificed. Fortunately, a ram was provided instead. David intentionally chose to go to battle against Goliath, and Jonah intentionally tried to run away from God's call for him to prophesy in Ninevah.
The new testament also has good examples of people demonstrating free will. The disciples chose to leave their jobs and follow Christ. Judas chose to betray Jesus in return for a financial payoff. Paul's letter to the Galatians has a really good verse that emphasizes that people have free will. The chapter and verse is Galatians 5:13 and encourages people to use their freedom to serve one another in love rather than indulging in the pleasures of the flesh. John 7:17 has John challenging people to choose to do the will of God. Proverbs 16:9 says that humans will plan their course.