There are a couple of things you can try.
Run something like CCleaner (http://www.piriform.com/ccleaner) to clean out temp files.
You could also try clicking on start, type msconfig, press enter, and disable any programs that you don't use that may be running in the background. Be careful not to disable any services necessary for Windows to run. If you are not sure what it is then "Google" it to see what it is before you disable it.
If you are not using an SSD you could also try defragging the hard drive.