Where can I get free software to optimize my pc?

What are you trying to optimize. Windows 7 has several tools built into it for optimization.

You can run disk cleanup and disk defrag (which automatically runs in windows 7.

If you are looking to clean temp files you can try running ccleaner. http://www.piriform.com/ccleaner

You can also run several spyware scans using either malwarebytes antimalware or superantispyware.

Other than those tools you would have to start purchasing software which may or may not “speed up” your PC.