I can understand not wanting to open up the laptop. Are you able to install Windows from scratch? If not, then you can at least make improvements by uninstalling unneeded apps and disabling unnecessary services. Delete any unneeded user files from the drive to free up space. You can improve performance by adjusting Windows settings such as reducing display effects. I suggest changing Folder Options settings so that it will always show file extensions (default is to hide file extensions). I believe that it's better if users see file extensions so that they will recognize when a file extension is of a risky type (e.g. .exe, .com, .msc, .reg).
Hello! My son is heading to college and has an Inspiron 15 with core i3 processor and 8 gb ram and a T of storage.  I want to see how he starts off with college before  making the investment on a better computer.  I feel like I just need to make it quicker and delete files and high school apps that he no longer needs.  Any suggestions on how I can do this myself and not incur a huge expense?  
Clean Up Old Computer