There are different ways:
1. Open the Run box by pressing [Windows button] OR clicking start > Run.
Type msconfig and hit enter.
Click the Startup tab.
Here you see the programs that run at startup. Remove the programs that you dont want.
2. Another way:
Click Start > All Programs > Accessories > System Tools > System Information
Expand the Software Environment branch
Click Startup Programs
Remove the programs that you don't want at the startup.