Here's a step-by-step guide:

1. First, turn off the water supply to the toilet. The shut-off valve is usually located behind the toilet bowl, near the wall.

2. Remove the lid of the toilet tank and set it aside.

3. Locate the old toilet handle and disconnect it from the toilet tank by unscrewing the nut or bolts that hold it in place.

4. Once you've removed the old handle, take the new handle and insert it into the hole in the tank where the old handle used to be.

5. Secure the new handle in place by tightening the nut or bolts with a wrench. Make sure the handle is straight and secure, but be careful not to overtighten it, as this can cause damage to the toilet tank.

6. Attach the chain or lift wire to the new handle, making sure it's the right length so that it will flush properly.

7. Turn the water supply back on and test the new handle by flushing the toilet a few times. If it flushes properly and without any leaks, you're all set!

If you have any trouble or need further assistance, don't hesitate to reach out to me or a professional plumber for help.