I need best software to make computer faster

My PC has been crawling this past few days. I have already done an anti-virus check, defragmented my HDD's, cleared browsing history. It's still the same after reboot. What is the best software to make computer faster? Could it also that I need to upgrade my memory? I have Intel COre i3, 2 GB RAM, 500 GB HDD and Windows 8.
