If your computer has gotten slower and hot to the touch, it may be infected with malware. Malware can monopolize a computer’s resources and make it overheat and become painfully slow.
Before you try anything invasive - like replacing the hard drive - try running a good anti-malware program on your PC. Malwarebytes has a free version of anti-malware software on their website that you can download and run on your system.
You may also try defragmenting the hard drive to make it run faster. Type defrag.exe in the Search Box on the Taskbar at the bottom of your screen to open the “Defragment and Optimize Drives” app. The app will offer options you can click on to optimize your hard drive.