Run cleaner to clear out Temp Internet files, system cache etc
Go to Registry Section, run scan and have it clear out registry keys that are no longer needed.
You can also go to tools and dissable any startup items that are not necessary.
(if the enteries are microsoft, intel, nvidia, ati, broadcom, atheros, then leave them enabled, also leave your printer enabled).
Download Auslogics Disk Defrag
Defrag your C drive as it is probably very fragmented