PC performance optimisation and cleanup (This is specifically for Windows, but should be similar for other OS's although application names will be different)

1. Run msconfig, click on the Startup tab and uncheck any unnecessary startup items.  When done click Apply.  If asked if you want to restart select not now.
2. Run Windows Defender or Malwarebytes to check for any computer viruses, worms, trojan horses, ransom-ware, spyware, adware, scare-ware, and other malicious programs.
3. Go to Windows Update and check for any updates that need to be installed.
4. Run Disk Defragmenter for all drives, please note this can take quite a while.
5. If you are more advanced remove unnecessary items from the registry for applications that the uninstaller left behind when removing them.
6. Restart the system in order for the changes to take effect.