ccleaner. download that and run it. do the registry cleaner too.
download smart defrag and run that too.
delete uneeded things from your hard drive. if it gets to full it slows down a lot.
uninstall programs you dont use.
type msconfig in the search bar and go to startup and deselect every program that doesnt need to be started when you start the computer.
clean out the cpu fan by spraying compressed air into the fan openings.
learn how to use google cause this is a heavily documented problem to fix.