How to replace a muffler?

The muffler will need to be cut out (hacksaw) and a new one welded in or clamped in. Here is a kit that you can use to do the job.

Also, use WD40 on the clamp and hanger nuts a bolt and let it sit for a while.

https://amzn.to/41RVCcK

You will need to jack the car up, here is a guide to help with that:

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

Please upload pictures or videos in your response of any problems so we can see what to help you with.