This video demonstrates how to remove and replace the bathtub spout. To replace your spout simply remove the spout.
1) Remove the Lock screw on the bottom part of the Spout.
2) Remove the Spout from the feed pipe.
3) Go to your local plumbing supply store and acquire a new replacement part to install.
Watch the video for a demonstration and special considerations.
This will NOT fix a leaky faucet. If you have a dripping faucet then you need to replace the actual valve (the on/off hot/cold part). A leaky valve is a lot more involved and you would need a plumber.
Tub Spout : https://amzn.to/3cmXBd6