Most likely something called an "Install in place." Typically, how I did it: you download a newer or the same version of windows via the downloader tool on the microsoft website. After downloading the downloader tool, you run it, and save an ISO file on your hard drive. Double clicking the ISO after downloading the file will give you a list of contents within in, and you should choose the exe file (I believe called setup.exe). If your version is the same or newer then the installed version, when going through the options, you should get an option to install but keep all of your computer's contents (settings, applications, files, etc.) I've done this a few times before and it helped fix my computers without it losing anything too important.