While using internet from computer, you will have to run plug-ins and give permissions in many aspects. This will automatically install many unwanted programs and software in your computer. Consequently, these will reduce the speed of your computer. It doesn't mean that deleting the programs from the respective folder will help. You ought to remove the installed files properly. It is recommended that you check the list of programs that are installed regularly and remove the unused ones. Check out how to remove installed programs in Windows.