My mother’s laptop has been running as fast as a turtle on a snail going uphill for a long time now. Everything has been done to it, including formatting it and installing another, less cumbersome OS, but nothing improves. I have an HHD available, I have done some tests and it does work.
Would changing the hard drive do any good?
Is the hard drive failing and constantly blocking reads and writes? Maybe, check the SMART data.
Is the cooler full of hair/fur/dust and clocking the CPU down? Maybe, look at the thermals etc.
If you don’t diagnose issues you are just guessing and potentially wasting money replacing parts that are fine.