Q: How Do I Get a Security Clearance Upgrade?
A: The determination about what classification level is needed for your position is based on federal government requirement. An individual may find themselves in a position where they are working with a public trust or secret security clearance, and then need to obtain access to a higher classification. The federal government will determine whether you have reason, and characteristics, for being involved in a federal program with that requirement, or not. There must be a federal need that is being met for an individual to get a clearance, no matter what level.
If the federal government does need you to be in a job requiring a higher classification access, congratulations, your life gets put under a government-issued, government-run, microscope. Specifically, the US federal government becomes very interested in your whereabouts, activities, associates, and friends during the last ten years, talking with your associates and friends face-to-face, if possible. This interview process is part of a Single Scope Background Investigation (SSBI), used to determine if you have the characteristics necessary for working at a Top Secret level. In contrast to a secret or public trust investigation, where the checks are largely automated, an SSBI involves more scrutiny and more time.
Investigators normally use the references you listed on the Standard Form 86 (SF-86) for your initial clearance application and go a little further in their investigations of you. They ask your SF-86 references for references who might also know you, and then interview those references of references. As you can see from this process, a government need for someone to work at a higher level of classification is not necessarily a guarantee that you, specifically, will be granted access to a higher classification level–even if you meet the work requirements. The decision also depends on your SSBI results.